Death traps. I have always struggled with big set piece death traps. I can do puzzles practically on the fly, but death traps just give me trouble. Maybe they're more of a film trope than a D&D trope?
Are you familiar with the Five Room Dungeon model? I'm using that right now, as my players' characters enter Midwood's big megadungeon at long last. They're only going to retrieve a McGuffin -- they don't have time to clear the joint out, with a kobold invasion about to happen -- so once they've hit all the obstacles I've got planned, the next likely room they explore will have what they were looking for. As long as you're not too obvious about it -- and there's no reason for the group to clean out every nook and cranny of the joint -- it should be a pretty invisible way to make this more bearable for you.
[MENTION=4475]Sammael[/MENTION] I really second this advice, and in my last campaign I used a "5 room dungeon" to great effect.
[sblock=Drowned Amandtwer]
Drowned Amandtwer was an old northern keep which had been flooded by enemy forces seeking to quell an insurrection. Once it was the proud focal point of resistance against an evil empire, where feuding lords and warring races made peace and swore their swords to each other. Now it's ruins are half sunken in a frosty marsh/lake and haunted by the spirits of those who perished within. The PCs arrive in search of a magic crown kept by an oracle there.
1. First they face getting access to the dungeon - the entrance is guarded by an enemy military camp replete with slaves. The PCs infiltrate as slaves and get posted digging graves for slaves who died trying to enter the trapped puzzle door. Through wit and trial and error the PCs best the puzzle door and evade pursuing guards.
2. Second they face a wraithly guardian and it's drowned followers, then get information from the guardian once it is defeated. Side chambers here are optional but allowed the PCs to (a) get a map of the dungeon or (b) gain a type of spirit sight to witness ghostly events. The PCs then faced a choice of three passageways, all of which seemed to lead to their final destination...
3. Third, the PCs decided to enter the crypt of a saint once allied with the rebel alliance. They fought off shades seeking to consume a lingering spirit protected by dark guardian angels. The PCs helped find proof of the lingering spirit's dead children, thus allowing her to go on to the afterlife. They gained an amulet which pointed them toward the location of the crown.
4. Fourth, they decided to explore another of the passages, confronting a room of trapped wights who'd been trapped within the flooding room by the lingering spirit the PCs had just released in a desperate bid to save her child. They learned the wight were actually 2 camps: traitors and those wrongly accused as traitors. The PCs sided with the wrongly accused to defeat the traitors, learning the waterworks were sabotaged to flood the old keep - to reach the oracle the PCs would need to access the waterworks first.
5. Fifth, they went into the last passage entering an audience hall where treaties were signed and the leaders of the rebel alliance had sworn blood oaths to each other. Here they fought a dangerous blood golem, and were badly beaten up as they didnt solve a riddle to deactivate dark magic empowering the blood golem. Ghosts revealed that the oracle they sought was a dragon.
5.5. A mini-encounter based on the waterworks involved a mathematics puzzle / skill challenge.
6. At the aerie where the crown was kept they faced a dangerously unbalanced stone bridge and a swarm of bugbears and blackcloak soldiers serving one of the main villainesses. After defeating her they were faced with solving the puzzle of where the crown was. Their amulet pointed to a font of water which had nothing inside it save water; however eight pillars surrounded the aerie each with a crown hovering in blue flames. Each pillar had a virtue of kingship written on it. The catch was they had to solve the puzzle before the oracle dragon showed up.
6.5. This was a dénouement, though it could has been a fight. The PCs negotiated with the oracle dragon who agreed to let them take the magic crown only if they were agreed in which contender tithe throne they would support.[/sblock]
