Gate (ruins)

The Gate was a set of ruins situated in the Frost Hills.

Description
Underneath these ruins was an immense, black cube with a single door. Within the cube were several colored stone slabs that acted as doorways to other planes and even other Prime Material planes.

Inhabitants
In the 14 century DR, these ruins were inhabited by a group of powerful bugbears, led by a smallish beholder by the name of Zythalarlr or "the gatekeeper." Those who desired to access the gates within the black cube had to answer a riddle from him, otherwise they would be killed and eaten.