Lair of the Lich Kings

A vast plain interspersed with areas of smoothed stone 500 feet across. Under each multi piece stone slab, is an inverted pyramid of stone. At the tip is a coffin sized area where the previous heroes of legend have imprisoned the various Lich Kings. These powerful diabolical sorcerers, have appeared periodically across the millennia. No one in living memory can remember the first one. During that period of eternal imprisonment, the Kings have learned how to cooperate and wreak havoc across the surface, across the sparse expanse of the Nemyrothean plains. No explorer has survived trying to count them all.