An underground temple, sundered by a great chasm from an ancient quake.
The party was asked to clear this out to allow their rat folk allies to take residence.
The temple held many such wonders, a mysterious chess player who challenged when appeared, a room full of noisy fungi, and a cavern with a cyclops statue bearing a great gem as its single eye.
Here the party became enchanted by a gaggle of harpies, all but one of their number charmed, who managed to gain some allies and defeat the bird-human hybrids and free them from the spell.
A possible location for a second place of residence, as it was free for the rat folk to move in.