Nirnroot (Oblivion)

Nirnroot is almost always found near a body of water, and has a number of peculiarities, particularly its ability to glow in the dark and emit a low buzz or hum, as well as its inability to regrow after being harvested.

Biology
Unlike every other plant in the game, Nirnroot does not regrow; each plant can only be harvested once. Consequently, Nirnroot is a rare plant - in fact, so rare, that no alchemist recognizes what the plant is except a man named Sinderion, located in the basement of the West Weald Inn in Skingrad.

Weak Elixir of Exploration
Sinderion will require 10 Nirnroots for the first potion, this will create a Weak Elixir of Exploration which gives you Night-Eye for 300 seconds and Fortify Health for 300 seconds.

Moderate Elixir of Exploration
Sinderion will tell you that he will require twenty Nirnroots for a Moderate Elixir of Exploration which gives you Night-Eye 300 seconds, Fortify Health for 300 seconds and Fortify Fatigue for 300 seconds.

Strong Elixir of Exploration
Sinderion will tell you that he requires another thirty Nirnroots to create a Strong Elixir of Exploration which gives you Night-Eye for 300 seconds, Fortify Health 20 points for 300 seconds, Fortify Fatigue 20 points for 300 seconds, Fortify Blade 5 points for 300 seconds, Fortify Blunt 5 points for 300 seconds, Fortify Destruction 5 points for 300 seconds, Fortify Restoration 5 points for 300 seconds and Fortify Sneak 5 points for 300 seconds.

Grand Elixir of Exploration
Sinderion will tell you that he requires another forty Nirnroot to create the Grand Elixir of Exploration which gives Fortify Health 20 points for 300 seconds, Fortify Fatigue 20 points for 300 seconds, Night-Eye for 300 seconds, Fortify Blade 10 points for 300 seconds, Fortify Blunt 10 points for 300 seconds, Fortify destruction 10 points for 300 seconds, Fortify Restoration 300 seconds and Fortify Sneak 10 points for 300 seconds.

Every time that you bring Sinderion the Nirnroots you need for the potion, it takes 24 hours to claim your new elixir.

Number of plants
There are a total of 306 Nirnroots in Cyrodiil (263 outdoors, 43 indoors). Simply paying attention to shorelines and potted plants while playing the game will normally yield a significant number with no extra effort. The game makes it easier by making a certain sound or harmonic near the location of a Nirnroot.

Locating them
Most natural Nirnroots are found near bodies of water. Some are found in various buildings throughout Cyrodiil. Note that if you listen carefully, you can hear a faint, pulsating noise near the location of a Nirnroot.

Quests
Seeking Your Roots. To begin this quest, speak to Sinderion in the basement of the West Weald Inn in Skingrad or harvest Nirnroot for the first time.

Anvil

 * One can be found inside Heinrich Oaken-Hull's house. It's upstairs in the bedroom.
 * One can be found on a dresser in Dairihill's quarters in Castle Anvil's private quarters.
 * One can be found on a windowsill in Ulfgar Fog-Eye's quarters at the lighthouse.
 * One can be found near the statue at the lake left of the outer gate when entering Anvil.
 * One can be found on the edge of the water on the beach when walking from the lighthouse and approaching the gate to Anvil. Just beside the stairs to the docks, near some rocks.
 * One can be found just outside the Anvil City Gate, between the rocks nearby, hidden in a bush.
 * One can be found on the small island (has a chest on it) south of the lighthouse
 * One can be found in Smuggler's Cave beneath Castle Anvil.
 * One can be found on the small island just south of Castle Anvil.
 * 2 can be found on the small island west of Anvil.
 * One can be found to the north-west of the Anvil Lighthouse near the little gulf.

Bravil

 * Two can be found in Bravil. One is just Southeast of the The Lonely Suitor's Lodge, up against the wall. The second is behind the mage guild, right across the river.
 * One can be found in the 3rd Floor of Silverhome on the Water (the western door, its locked, hard.)
 * One can be found in the 2nd Floor of the Bravil Fighters Guild on a wardrobe.
 * One can be found while doing the Arrow of Extrication quest, in the Bravil Wizard's Grotto. Look at the map on the quest page to watch the exact location.
 * One can be found in City Swimmer's House.
 * One can be found in Andragil's House in her bedroom on the dresser.
 * One can be found at the southwest corner of the walls surrounding Castle Bravil,on a small island on the other side away from the wall.
 * One can be found West of the main gate, near a bridge over the river.

Bruma

 * One can be found on the second floor of Baenlin's House, in the master bedroom.
 * One can be found in Regner's House, downstairs on some crates.

Cheydinhal

 * One can be found in Down inside the Mages Guild Well. Requires you to perform the Cheydinhal Recommendation Quest in order to receive the key to the well.
 * One can be found under one of the bridges in town. The right bridge of the two to the south.
 * One can be found on the second floor of Riverview.

Chorrol

 * One can be found in Vilena Donton's house on the third floor in her bedroom. It's in a potter's plant next to her bed.
 * One can be found in Casta Scribonia's house on the second floor on the shelf to the right.

Imperial City and the surrounding isle

 * One can be found on the hill south of where the Imperial Prison Sewer comes out.
 * One can be found just east of Imperial City Sewers – North Exit
 * One can be found if you go inside Imperial City Sewers – North Exit and enter the first door to the right. Initially this door is blocked but it can be opened by turning the wheel inside the adjacent chamber. When you open the door and enter the room the Nirnroot will be just to the right from the entrance in the water next to small stairs.
 * One can be found by the dock outside of Vilverin.
 * One can be found on the back bench of The Gilded Carafe in the Imperial City Market District.
 * One can be found in the South Watch Tower's Captain's Quarters accessible through the Temple District and Arena.
 * One can be found in the pond to the left of door leading to Green Emperor Way in the Imperial City Arboretum.
 * One can be found in the Mage Quarters at the Arcane University. Inside the Southwest room on the first floor in a pot.
 * One can be found in a Planter in Archmage's Private Quarters in the Arcane University
 * One can be found under the water where the Sacred Lotus plants are in the Imperial City Temple District.
 * Three can be found in the Waterfront District, at the north end of the docks on the beach near the pirate's ship, named The Marie Elena. There is another one inside the ship itself in a planter on the desk near the enterance of the ship, but the pirates may become hostile if you board. The third is at the far southeast end of the small island.
 * One can be found south of the mainland-connecting bridge to Imperial City
 * One can be found on a peninsula north of the mainland-connecting bridge to Imperial City
 * One can be found in the Private Quarters of Samuel Bentien's House in Talos Plaza.
 * One can be found by the dock north of Weye.
 * Take a walk from Fort Magia to Culotte whilst looking near the river bank. There are seven at least, easy to find.

Leyawiin

 * Two can be found just east of Ahdarji's house by the walls (near the gate to the castle, one just south of the SW gate, one just north)
 * One can be found just east of Best Goods and Guarantees next to some rocks.
 * One can be found in the Blackwood Company Hall, on the second floor.
 * One can be found in Jeetum-Ze's room of the Blackwood Company Hall.
 * North East Gate
 * One can be found outside the Leyawiin North East Gate along the wooden dock just northwest of the gate
 * One can be found in the rocks east of the Coast Guard Station just outside the Leyawiin North East Gate
 * One can be found within Leyawiin, east of the North East Gate, by the pool of water
 * One can be found hidden amongst the grass near the water before entering Castle Leyawiin.
 * Take a walk, starting from left bank of Topal Bay and follow the beach untill you reach Leyawiin-Castle to find more of them.

Skingrad

 * One can be found in the the Surilie brothers' house in Skingrad.
 * One can be found on the third floor of Toutius Sextius' House in Skingrad.

Region Locations
Generally speaking, one can walk or ride along any major or minor body of water and find Nirnroot growing. Sometimes they grow between rocks or behind trees, and so require a bit of searching, but most often they are found relatively out in the open. Traveling along the Niben between Leyawiin and Bravil will yield quite a few Nirnroot.

Blackwood

 * At least five can be found around the water edges south of Fort Teleman and the nearby Gate to Oblivion, search carefully!
 * At least six can be found near and east of Fort Doublecross around the water edges.
 * One can be found just south of Tidewater Cave along the beach.
 * Three can be found along the southern beach of Topal Bay, west of the Niben River, in extreme southern Cyrodiil.
 * One can be found south of Bogwater camp in southern Cyrodiil, along the beach.
 * Two can be found on island southeast of Bogwater camp.
 * Two can be found on an island connected to the mainland by a bridge slightly southwest of Bogwater camp.
 * One can be found west of that same bridge, along the coast.
 * Two can be found in the wilderness, southeast of Bravil, south of Fort Irony. It is on the southern edge of the peninsula. Follow the coast until you see a derelict, burnt-out house on a small island, connected to the mainland via a bridge. One Nirnroot will be on the island, one will be immediately north of the bridge.
 * One can be found on the north side of Fort Irony.
 * One can be found about halfway between Fort Redman and Fort Irony, between Leyawiin and Bravil. It's on an island north of a bridge crossing the river (the map shows it's a peninsula, but it is in fact an island).
 * One can be found across the river of Fort Redman.
 * One can be found on the water's edge of the southern inlet, due north of Leyawiin, southeast of Bravil.
 * One can be found at the Black Dog Camp, following the Panther River, between some crates.
 * One can be found just south of the camp, along the river
 * One can be found at the base of a tree along the beach of the settlement Water's Edge.
 * One can be found south of Bloodmayne Cave between some rocks along the Larsius River.
 * One can be found along the northern shore of the Panther River, just north of the small letter 'n' in "Nibenay" on the map.
 * One can be found at the Ayleid Ruin of Veyond.
 * Two can be found on a small island with a dock northeast of Undertow Cavern.
 * One can be found just down the southern path of White Stallion Lodge, next to the dock and boat.
 * One can be found just outside Amelion Tomb.
 * One can be found next to the water down the steps next to Kindred Cave. Look underneath the wooden platform.

Colovian Highlands

 * One can be found west-southwest of Chorrol, near the end of the Black Road, near a pool of water with a boat.
 * One can be found at a pool with a waterfall south of Infested Mine.
 * One can be found by a small pool of water and waterfall just northwest of Black Rock Caverns.
 * One can be found inside the Battlehorn Castle, behind the stuffed Wolf.

Great Forest

 * One can be found in Torbal the Sufficient's House at Brindle Home.
 * One can be found at the bottom of a waterfall off Orange Road (just north of the letter "a" of the word "Road" on the map).
 * One can be found in house of Natch Pinder (2nd floor) in Hackdirt.
 * One can be found next to the firepit southeast of Fort Virtue.
 * At least three can be found at the lake in Shadeleaf Copse.
 * One can be found in Odiil Farm, inside the building (locked).
 * One can be found at Fanacasecul.
 * One can be found between some rocks underneath a tree along the White Rose River (just north of the letter "R" for "river" on the map).
 * One can be found along the White Rose River, just north of Fort Roebeck.
 * One can be found along the western fork of the White Rose River, before it empties into Lake Rumare.
 * One can be found in Shafaye's House at the Pell's Gate settlement south of Imperial City isle.
 * One can be found on the southwestern corner outside of The Sleeping Mare at the Pell's Gate.
 * One can be found south of Imperial City, just beyond an un-named bridge (northwest of Sardavar Leed).
 * One can be found outside of Sardavar Leed itself, by the water and rocks.
 * One can be found beneath the Old Bridge landmark.
 * One can be found just outside of Charcoal Cave, at the top of the waterfalls between rocks.
 * One can be found just south of Charcoal Cave, around the pool of water and behind a bush.

Gold Coast

 * Two can be found along the western coast of Cyrodiil, just north of Anvil.
 * One can be found on a small island off the western coast of Cyrodiil, north of Anvil.
 * One can be found by a shipwreck on the western coast of Cyrodiil, on a peninsula where the Brena River empties.
 * Two can be found on an island to the west of Anvil.
 * One can be found on an island south of the Anvil castle near Smuggler's Cave.
 * One can be found on the larger island south on the Anvil peninsula at the edge of the map.
 * One can be found on the coast to the south of Anvil and south-west of Gweden Farm.
 * One can be found on the large island where the Strid River empties into the Abecean Sea.

Heartlands

 * One can be found at a pool of water south of Roland Jenseric's Cabin. It's just south of the Blue Road, near some water hyacinth. it's a bit north of Nagastani.
 * One can be found at the edge of the water just down the hill from the entrance to Culotte.

Nibenay Basin

 * One can be found along the river near Vahtacen.
 * One can be found on the eastern beach of Lake Canulus.
 * One can be found outside Leafrot Cave.
 * One can be found on the beach of Lake Poppad, east of Muck Valley Cavern, and slightly northwest of the Vaermina's Shrine.
 * One can be found outside the door to Fort Entius, at the head of the Silverfish River.
 * One can be found in the little bay going south from the head of the Silverfish River.
 * One can be found north of Peryite's Shrine at the top of the waterfall.

Nibenay Valley

 * Two can be found near the wooden bridge by Imperial Bridge Inn.
 * One can be found on the shore of the Bawn elven ruin
 * One can be found on the island off of Bawnwatch Camp, near Bawn
 * One can be found south of Bawn just before the bridge. Right beneath where it says 'County Bravil' on the map.

Valus Mountains

 * One can be found on second floor of Lord Rugdumph's Estate.

West Weald

 * One can be found about halfway between Kvatch and Ra'sava Camp near a small pool of water.
 * Two can be found by the small pond just east of Shardrock.
 * One can be found on the western side of a small lake between Kvatch and Miscarcand.
 * One can be found by a small pond just northwest of Skingrad, south of the Reman Rune Stone. (At the center of the letter 'k' in 'Skingrad' on the map.)

Other Locations

 * Two can be found by the upper pool west of Barren Cave.
 * One can be found by the docks where you hunt for slaughterfish in the Go Fish quest.
 * One can be found in the Hunter's Run during the Caught in the Hunt quest - after killing the first hunter, jump in the water and swim.
 * One can be found on the south side of Morahame.
 * One can be found inside Fort Cedrian.
 * One can be found inside Frostcrag Spire Living Area.
 * One can be found at Fort Homestead, along the northern walls and beach.
 * One can be found at Veyond Black Waters, along the northern wall of the second chamber.
 * One can be found on the desk in The Vile Lair study area. This Nirnroot is unique as it is the only one found in "picked" form instead of growing. It looks similar to a bright green chili pepper. NOTE: It is also the only Nirnroot in the game that regenerates. After about a week there it will appear on the desk again along with any other loose ingredients in the lair.
 * One can be found to the left of the entrance to the Caldew Chapel.

Console
Using the console on the PC version, you can also add them by using the cheat:
 * In the german GOTY: Nirnwurz (Nirnroot): Console-Code: 0004E940
 * In the german GOTY: Nirnwurz (Nirnroot): Console-Code: 0004E940

is the amount you want.