Our group has never tended towards "dungeon" play. I think in 17 years of gaming, we've had no more than 3-4 dungeons that took more than 1 session to complete(though if you count sci-fi games on spacecraft, that number increases dramatically).
The highlights would be:
[sblock=Koganusan]The largest dungeon our group has ever done was when our group hit Paragon in our first 4e game and our DM turned
Koganusan into a massive dungeon. It was great because he took actual journals from the write-up, actual art elements from the game, and made a flow-chart map of the place so we could go almost anywhere.
The little bits and pieces from the AAR gave the place a
ton of flavor that made it seem really real, and the fact that we were given descriptions of art on wall carvings and treasure we found made it even more immersive. For example:
"The wall panels are covered with pictures of dwarves kneeling before elephants with plaintive gestures. The elephants are trampling the dwarves.
The bracelet is engraved with pictures of a mandril menacing a dwarf. On the inside is an image of a water flooding a dwarven dining hall."
It was also hazardous as hell. For example:
My ranger got hit by a nasty trap that hit you with a bear trap round one, the bear trap shot up 30' into spikes on the cieling on round two, a nozzle bathed you in flame on round three, and then the bear trap let go and retracted with lightning speed on round four, causing you to fall 30' and start it over again. He managed to step into
3 of those traps in one fight(he's a bit impetuous).
It was awesome. The dungeon having a rich history really came through to the point where uncovering more bits of the story of what the hell happened there was our prime motivation - over treasure and xp even; remarkable for our group of powergamers.[/sblock]
[sblock=Starship sabotage]In the (only) GURPS sci-fi game I ran, the group were all the entourage of a diplomat on a starship heading to a colony that was seceding from the empire. On the way there, terrorists sabotaged the hyperdrive and blew up most of the crew deck, leaving the players as the only really capable people in a crew of civilians able to stop the terrorists. It had some neat moments like:
*A 0-g fight in a hallway against a military-grade cyborg with magnetic clamps anchoring it.
*A desperate battle in the engine room when they leaped out of a crawl space and had a point-blank range battle where every bullet miss could damage a critical engine component and leave them stranded permanently. It got more exciting when the fire suppression system came on, blanketing the room with foamy fire-suppressant "snow" and reducing visibility to 5' - and then gravity generators kicked off again...[/sblock]
[sblock=Mini level 1 TPK dungeon]I did manage to *almost* TPK a group of 1st level adventurers with a dungeon that consisted of:
*a 30' ladder leading to the beginning of the dungeon - unfortunately, the last 5' had broken off and required an acrobatics check to swing to the platform from the last rung and avoid a fall into a spiked pit
*a 10' wide, 20' deep pit
*a 10' wide, 10' deep pit with spikes in it and a portcullis that slammed shut whenever something was leaping across the pit (requiring fast action to avoid bouncing off of it and falling into the pit)
*a skeleton on the far side of the portcullis throwing puny magic missiles at them the whole time (they had no one with a ranged attack)
It was like a comedy of errors. They ended up killing the skeleton with rocks and the paladin dragging everyone else's unconscious or dead bodies back to the surface(everyone fell into at least 1 pit and several were dropped in them accidentally while unconscious).[/sblock]
There are a few more, but the main things I've learned from these few experiences we have had with dungeons are:
[sblock=Notes]*If you have traps, make them mostly visible challenges rather than "screw-you" wandering damage. This also psychologically prepares the players so when an unspotted trap
does go off, they are annoyed that they missed it rather than annoyed at the DM for springing something out of the blue at them.
*Environmental effects make encounters more tactical and/or limit options - environmental effects that don't start until the middle of the encounter make it more dramatic (flooding with water, walls/scaffolding collapsing, rain/snow/equivalent suddenly falling, etc).
*An environment with a bit of real world (I.E. grounded in the game's history) detail, a story, and some element of mystery or unknown behind it will pull players in to a dungeon faster than the most fabulous treasure or expectation of experience.[/sblock]
So, in summary, my ideal dungeon would be:
*realistic
*lived-in
*grounded in the world's history
*mysterious
*dangerous