This is a room in one of my dungeons. I used it in a 20'x30' room, with the 30' walls on the north and south walls, and the 20' walls on the east and west. The solitary door is on the east.
Along the north and south walls of this room is a two foot high, one inch thick strip of bronze. Beaten into this bronze are black-on-bronze pictures of death. There are scenes of knights hacking off heads, wizards hurling fire at their foes, archers letting off a volley of arrows at another army, a gladiator stabbing another gladiator with his trident, bodies trampled under horses hooves, and more. Above the strips of bronze are lit torches. On the west wall is a sheet of bronze covering the whole wall, with a depiction of Mors, God of Death (or whichever god(dess) of the dead/death you want), on his horse, on it. Hanging from the ceiling (by a solid rope) is a black orb. At the foot of Mors' horse is a pile of money. If the players take the money, then the orb will send pulses of light at the bronze sheets on the north and south walls. Once this happens, all of the pictures of the dead people animate, and emerge as zombies. In the first round, the majority of the zombies will come out. 1-6 (or however many you want) zombies will emerge every three rounds after that. Each zombie should be as strong as needed, to either give the delvers a threat, or easy meat. The zombies will not leave the room. If the orb is shot (with an arrow, stone, etc.), then it will explode (all that magic inside it has to go somewhere), destroying all the zombies in the room (though not halting creation of more zombies).
The general idea for the PCs to do is huddle, fighting zombies, until they either think their way out, or get killed. One idea for them is to create a wall of flames (with either a spell, or oil and matches/spell) so that they have time to think. If this is done, the zombies will suicide into the flames, and will kill themselves faster then they are made. If the PCs wait long enough (throwing down more oil as needed), they should be able to run past the rest of the zombies and escape.
Another way would be to destroy the orb. This would kill the zombies, and if timed right, let the players waltz out. Of course, this would require an archer to not fight for a round (meaning if they miss, that many more zombies), and shoot at the orb.
Or the PCs could always simply try hacking their way throw the zombie hordes to the door and safety (or maybe that wandering monster who realized weak PC might stumble out...). The zombies should be strong enough to make this option possible, but inadvisable in the I-would-like-to-retire-and-just-maybe-see-a-couple-grandchildren-later-on-and-die-of-natural-causes area.
This room is not supposed to be a death trap (hehe, death trap- no pun intended), just simply a mechanism to get the players to use that underused organ: the brain. Especially since it might be better to simply walk away once they see, oh lets think, pictures of DEATH, a picture of the god of DEATH, a pile of unattended money (which usually means that either the they just killed something, or that there is a trap causing pc DEATH), a black orb (black orb=magic=DEATH), and that the money is in the west, which symbolized endings and DEATH. Yeah, walking away is a definite option.
Once, far back in the mists of time, there lived a great craftsman, Allscluptor. He was a genius at his art, the art of sculpture and architecture. He knew just where to chisel, and just how deep to make it. Masterpieces were made on his first attempt (which, in the real world, is next to impossible- the David took many different previous statues till the finished one). His work was so great, so lifelike, some say that, on cold, thunderous nights, they could see some of his work stretch, and get back into their original positions.
Allscluptor was called by a priest of Mors (who, in my world, are the people who do final rites, and are in charge of cemetraies. Nothing creepy. No necromancy. Mors frowns on that) to make a shrine to Mors. The perfect shrine. Allsclutor, after many refusals, and subsequent increases in payment, eventually agreed.
So he traveled to the city of H'taed, with a retinue of servants and mules carrying his materials and tools. And once he arrived, he set to work. And he built, and he built, and he built. And after many years, the room the priest of Mors provided was a perfect shrine to Mors. What that room looks like has since been lost to the ages. Once this was done, he took the payment, and left for his home (and, coincidentally, another job offer). But the city of H'taed made an enemy that day. A Necromancer, by the name of Ytinutroppo, knew about this perfect shrine. And he knew just how to take advantage of it.
Ytinutroppo raised himself and army of undead souls. Such an army that H'taed had no chance to defeat it. For every skeleton a H'taed soldier slew, 10 more sprang up. And for each H'taed soldier that died, Ytinutroppo gained another soldier. H'taed was soon defeated. And the shrine was taken. The necromancer walked into the shrine, and marveled at it. And he saw the proof of what he needed: the pictures of death moved. And so he began dark rituals, rituals that lasted night after night. Rituals involving the most horrific of materials. Dread rituals that a small band of PCs tried to stop, but got killed by a bunch of skeletons before reaching the shrine. And then Ytinutroppo finished, on a dark and stormy night. He had finished, and created the Death Room, from which he could raise a demon so powerful gods would flee before it. He raised Nomed (he's so powerful he doesn't need to show off with a ...the bloody).
And then what happened? Ytinutroppo rule the world, with Nomed as his servant? Well, another small band of PCs found out about the first groups mission, managed to get through the hordes of undead, and reach the shrine. These PCs found out that Nomed doesn't like being some common servant, and didn't try to kill the PCs (Ytinutroppo forgot to mention who exactly to protect himself from, and Nomed is very, very crafty). And thus Ytinutroppo was slain in time, Nomed sank back into the depths from whence he came, and the PCs convinced the gods that they should at least change the function of the shrine. The gods, because they, too, don't like being bossed around by a bunch of PCs, followed the PCs intructions to the letter: they made it so that it summons hordes of zombies. And the PCs died a gruesome death. And the gods lived on happily ever after.
The rooms magic was soon figured out by other Necromancers. And those Necromancers made a copy of the room for their throne rooms. Eventually, the first room rotted, rusted, and fell, and became another victory for time.