The Wellspring Treasury is a dungeon found in the Frosted Hills in Act 1. (Found in Vanilla Torchlight 2 on Hardcore Elite NG+)
The monsters you can find there are electric bats, undead, and possessed ones.
There may be a Promising Fishing Hole.
It seems to have a high chance for mimics.
The entire dungeon is only one large floor with multiple champion monsters.
The last champion monster will drop a "Mysterious Gem".
At the end is a Statue. When you click on it, with the gem in your pocket, loot and gold is dropped around it.