The main tower and surrounding buildings were grown by Neloth with massive mushroom cuttings he brought from Morrowind some time before the eruption of Red Mountain. Although he grew the tower using Telvanni sorcery, his mycologist, Elynea Mothren, continues to nurture it.
Following the Levitation Act of 3E 421, levitation magic became outlawed throughout the Empire. Because all Telvanni towers used levitation magic to scale their heights, a different approach was required for Tel Mithryn. Neloth dealt with this problem by creating a magical device at the base of the tower stem. A small circular pad embedded with glowing runes acts as an elevator, channeling arcane energy from the runed plateau vertically through the hollowed out mushroom stem to a pronged focal point near the top of the tower, which is connected to the roof. This allows anyone to travel from the ground floor to the top of the tower in a mere matter of seconds.
The main floor of the tower is littered with arcane items, including various magical artifacts, potions, alchemical ingredients, spell tomes and other books about magic (all of which belong to Neloth, so taking them is stealing). There are also tables covered with various Dwemer artifacts and tomes about the Dwemer. Three smaller additional rooms are on the north, east, and south sides of the main room. These include a bedroom, a creature testing lab containing two caged Spriggans (regular and burnt), and an enchanting room, which also includes a Staff Enchanter.
- Black Book: The Hidden Twilight – In the same locked room as the Staff Enchanter, on the enchanting table.
- Ahzidal's Descent – On a table
- Bone, Book I – On a shelf
- Confessions of a Dunmer Skooma Eater – On a table
- Deathbrand – One on a table, underneath Ahzidal's Descent, and another on a nearby shelf
- Horker Attacks – On a table
- Lives of the Saints – On a shelf – On a shelf
- Nerevar at Red Mountain – On a shelf
- The Axe Man – On a shelf
- The Doors of the Spirit – On a shelf
- The House of Troubles – On a table
- The Poison Song, Book I – On a shelf
- The True Noble's Code – On a shelf
- Varieties of Faith in the Empire – On a shelf
- Words of the Wind – On a shelf
- Azra's Staffs – Retrieve one of Azra Nightwielder's staffs.
- Briarheart Necropsy – Study a Forsworn Briarheart for Neloth.
- Experimental Subject (Neloth's Health Boost) – Test out a new spell for Neloth.
- From the Ashes – Kill the Ash Guardian Talvas accidentally summoned.
- Healing a House – Repair the withered Telvanni tower.
- Heart Stones – Find a Heart Stone for Neloth.
- Lost Knowledge – Find a certain Black Book for Neloth.
- Old Friends – Find out who has been sending Ash Spawn to attack Tel Mithryn.
- Reluctant Steward – Locate Neloth's missing steward.
- Telvanni Research – Help Neloth in his research on Ash Spawn.
- Wind and Sand – Retrieve a book about the Alik'r Desert for Neloth.
- Experimental Subject (Silence) – Be the test subject for Neloth's new spell.
- Elynea's Ingredients – Find and deliver a rare alchemy ingredient for Elynea Mothren.
- Sometimes when entering Tel Mithryn the elevator may not work.
- Sometimes when first entering Tel Mithryn, the door to the staff enchanting room will be open, allowing the player to use the Black Book early.
- The room that houses the Staff Enchanter may re-lock itself after re-entering Tel Mithryn.
- Getting the Scribbles of a Madman that begins the miscellaneous quest "Locate the Black Book" after already having all the black books, it may tell the Dragonborn to go to Tel Mithryn tower to find the Black Book, thus making the quest impossible.
- Dialogue with Elynea Mothren
- Overheard conversation in The Elder Scrolls IV: Oblivion: "He's getting older, but he can still teach a bit about Alteration. He's been teaching it since before the Levitation Act of 421."
- Overheard conversation in The Elder Scrolls IV: Oblivion: "He still teaches, though he lost his passion for it after the Levitation Act was passed. Can't say I blame him."