The Tomb of Horrors and the Sting of Cyclic Redundancy

So this party entered the Tomb of Acererak the Lich, proper from the entrance inside the Black Academy, with the help Drake. They explored the main hallways and its frescos and friezes of demonic scenes of torture, battle, and suffering. They found their way to a portal filled with white smoke and a great green demon face. Having the Journal of the Tomb from the wizard, Desatysso proved a great bit of help. Finally they went through the portal only to arrive in a room with no exits. Secret doors led to crawlspaces barely big enough to admit them, more secrets to rooms with 3 obviously locked chests. Back to the main hallway again, despair. Find crawlspace in bottom of pit trap find hallway with many orbs. Some painted and some appear real but are illusory and conceal more crawlspaces. Secret door after secret door ... then finally a massive mutant four armed gargoyle attacking into a doorway. Searching, brain in a jar, just funny, because everyone but priest is undead again the party considers changing him. Large seesaw trap into flaming lava mostly easily averted. Find that when you go ethereal the entire Tomb is surrounded by hundred upon hundreds of demons and devils. Find illusory cobwebs and dust and fake tomb with fake Acererak easily disintegrated.  Find the path and Detect Secret doors turns them toward only the end. Great columned hall, throne, scepter path leads on, false treasure room find the path again points onward, so they ignore. Secret door, arcane symbols, stone bier, glittering gemstone encrusted skull which gets disintegrated. Massive pile of treasure in which they find half of the Amulet. The priest communes with Vecna and learns that this Tomb is but a mask of the true purpose which not even the Gods themselves can determine its true purpose. The 'thing" Desatysso came for was indeed physical remains of the lich, Acererak and the great green demon face was indeed the portal to the next act of Acereraks plan.

Going through they stand in a Promethean anti-landscape devoid of any horizon. with only flashes of silent lightning far overhead. Slender spires stand silent and entropied in the intense cold and the darkness. Thin walkways arch out to some spires at different levels.