A glome is a 4 dimensional sphere, the hypersphere version of a tesseract, a hypercube.
The heroes have destroyed the minions, plunged through the catacombs and defeated the guardians. They slowly enter the chamber to find the dark mastermind behind the scheme. The mastermind has a request for them, however:
"You must destroy me. To destroy me is to rid the world of a great evil, that is to say, me. But before you can destroy me, you must understand what evil is, what evil must be, why evil must exist."