I've not yet read the other responses, but . . .
. . . this is the way I would do it - every time they open a door, make a roll to determine which room they enter, with no chance of entering the room that contain(s/ed) the lich. To reach that room, they have to do something odd - like place items found in some of the rooms in a particular place in various other rooms. Considering how (un)likely they are to reach any of those rooms any time soon - even if they knew what to do - it will be a very long time before they reach that room - if ever.
Also, as this is meant to be a dungeon from which the entombed lich cannot escape, I would make it so that something similar is also needed to escape the dungeon. Otherwise they could be in there for a very very long time to come.
Now, as to more chaotic effects. Do you have the Manuel of the Planes? Each time a room is entered - even if it were entered before - roll on a table to see what planar traits are in effect (although perhaps major Chaos is always in effect, especially if the Lich were Lawful). So perhaps the room is minor fire, then the next is major Good, then the next major air, then the next - which by chance is also the first - major cold, and so forth. Have altering gravity at times (heavy, freefly, normal, this direction, that direction, etc) - perhaps (again) rolling for each room, even if the room has been entered before. Consider varying heat conditions (especially if you have Frostburn & Sandstorm - or 3rd party equivalents).
And have a really really random table (perhaps even using 2d% or more) for the creatures (if any) found in each room - so that perhaps entirely inappropriate creatures result, such as fire based creatures in a room that deals cold damage every round, for example.
What about differing time effects for each room. It won't matter until they are out of the dungeon, but perhaps when they leave they'll find that years have passed - or that they are in the past! - from all the different time effects they endured in the dungeon. Actually, the dungeon itself might be under an odd time effect as a whole, such that for every day within a year passes outside it. If nothing else, it would mean that the lich has not had as much time to try to escape, increasing the chance that its imprisonment truly would last for millennia, at the very least.
Hmm, what else . . .
- Should any PC attempt a listen check at the door, roll as if they were entering the next room to determine what (if anything) they hear. Then roll again when they open the door to enter.
- A low but persistant muttering / waling sound should be nearly everywhere. In some rooms it is deafening, while in others it is almost too low to be heard. All listen checks receive a penalty of [20 - d20], roll for each room.
- If a PC actually tries to listen to this muttering / waling, use sanity based rules (if you have them), or perhaps roll as if they were facing a Fascination effect, with the effect lasting until the other PCs shake them, etc. The save vs becoming Fascinated is DC 10 + d20. Perhaps, once awoken from the effect, they face a minor morale penalty of -(1d4) for (1d4) minutes? Hmm, that wouldn't effect a lich, but it would fit with the nature of pandemonium, I think.
- Any time a PC makes a Spot check and either 1) there is nothing there to spot, or 2) they fail by 5 or more, they seem to see movement out of the corner of their eyes for the next (1d4) rounds.
- Any attempts at Commune, Contact Other Plane, etc require a Will save vs Confusion for (1d10) rounds.
- Any attempt at Augury, or any other form of Divination vs what is beyond a Door always comes up Weal and Woe or the equivalent ambivalent response.
Does any of this help? Remember, this *is* based on pandemonium. You want it as chaotic as possible.
![:]](http://www.enworld.org/forum/images/smilies/devious.png "Devious :]")
