A small and straightforward level. Head into the mausoleum directly in front of you, entering to its central area and then crouching down the tunnel at the end of the corridor of bearded mascarons. Take the teleport and follow the stairs to where you can find the glass key.
The glass key door, though which you will find the pentagram, is on the east side of the level, and the exit pad is just a room over to the southeast.
