Note: This information was taken from TSR's original AD&D adventure, the Temple of Elemental Evil.

Rats

For the DM: At first glance this place seems long abandoned; dust, dirt, and cobwebs abound. A careful perusal shows, however, that several of the skeletons in the place are not old remnants, and some of the instruments and mechanisms have been used very recently indeed. Only if exacting care is taken in inspecting the floor can some drops of blood be noticed, leading south (the trail of a sloppy ghoul). Without this clue it is 90% likely that the secret door in the pillar will go undiscovered. Check only once per character looking, but roll dice as if normal checks were being made. (If the trail is discovered, apply normal chances of locating the secret door mechanism--1 in 6 for nonelven characters, 2 in 6 for elven).

Inside the pillar is a shaft some 30 feet deep, with iron rungs set into the stonework for easy descent. The rungs are obviously used with some frequency.