Stony Creek Cave

Located southeast of Windhelm, North from Riften, just north of Ansilvund. Contains Stone of Barenziah. If you are lost when you enter, climb up the rocks to your right and walk behind the pole with the Breton on it. Sneaky types beware- there are two enemies in a long straight passageway with nowhere to hide.

Loot

 * Moonstone Ore Vein (2)
 * Various chests
 * Finn's Lute - (Quest Item)
 * Unusual Gem - in the area where an alchemy table is.
 * Book Mystery of Talara, Book IV - Illusion skill book
 * Treasure Map X can be looted near the alchemy station.
 * Dynamo core - on top of a waterfall on the right hand side.

Related Quests

 * Bounty
 * Stones of Barenziah
 * Miscellaneous quest to return Queen Freydis's Sword to Oengul War-Anvil
 * Find Finn's Lute
 * Potential location for a miscellaneous quest to defeat a bandit leader for Brunwulf Free-Winter
 * Possible location for Meridia's Beacon

Secret

 * Going towards the end of the cave there is a dead end with a bandit, a chest and a waterfall. Checking the map reveals the path continues further. By climbing the rocks, so that you are higher than the cave mouth (on the opposite side worked for me, as a second opinion I prefer the large rock to the right), then using the Whirlwind Sprint shout, you can reach the top of the waterfall. At the end of the corridor there is a passage "to Kagrenzel". There is a flawless diamond on top of the second arch and a chest immediately after it with (leveled) items. This chest has also been known to contain a book required for the Winterhold Library quests. Atop of the waterfall that is directly to the right of the chest, and below the hole in the cave ceiling, is a Centurion Dynamo Core. There is a chest at the end of the tunnels near the surface of the lake, and a locked expert chest hidden in the water of the lake. Beware of the Falmer, their numbers and level are leveled as well.
 * It's possible (Although frustratingly difficult) to get ontop of the waterfall without using whirlwind sprint. To do so, run ontop of the rocks on the left side of the waterfall. By running forward onto the rocks and strafing left and right (A trick sometimes referred to as zig-zagging) and jumping, you'll be able to get to the top. It should be noted, however that the jumps need to be very precise and it's possible to fall through these rocks.
 * Additionally, swim underwater in the southeast corner in Kagrenzel - you will find a hole in the rocks, and you can swim outside of the map, and teleport to a different part of the ruins, where you can find a Strange Orb. If you touch it, it imprisons you for a while, and then drops back into the lake, through a long, vertical tunnel.Be careful, as you may be hit while falling and die. Instead of touching it, you may exit to Skyrim, discovering the location of Kagrenzel on your map - showing that this is not a secret, only you should travel through these ruins the other way, from Kagrenzel to Stony Creek Cave.