One of my designs from the late 80's, used with a high level group of players. Game rules were a healthy does of Arduin Grimoire with chunks of home-brew System 2 modifications. Some of the most dangerous creatures in play at the time were techno-liches, evil priests serving a death god who was the spirit of a transformed Saberhagen Berserker. I'm sure I'll get around to writing that up someday...
For this particular dungeon I'd sketched the entry way and used a rune-riddle on the door. The door is round and rolls sideways after unlocking, it's unlikely anything less than a greater Giant could force it otherwise.
The main level was fairly simple, but contained several classic traps and features. Nominal elevations are in orange, referenced to the bottom of the entry stairs. Encounter numbers are in purple. Area #12 has wavy greenish/yellow lines for floor to ceiling tapestries. Dotted blue lines show approximate paths of the water conduits.
All room descriptions will be generic, as my players still visit here occasionally.
Part of the fun of running this particular module was telegraphing certain events. Even when they could guess what was coming it still made them flinch. Between #2 and #3 is the odd rim around the corridor. It's the ball stop for the encounter in Area #16. Makes no sense, yet. The first pit is actually fairly minor, but as the water is super chilled the coating of ice on the vertical walls and rim makes it a good warm-up. Falling into the water is intended to be semi-lethal as it's super-chilled salty slush (about 28 deg Fahrenheit). Within seconds the character is coated and loosing body heat like nobodies business. That's when the ice-kraken attacks. I usually played it as a large enough monster the party can barely drive it off, but it doesn't stick around to be killed.
Note - it CAN get out to the fountain pool at Area #1 and or swim the internal water conduits.
Area #5 is where I really start messing with the players. Two Elven sets of plate (Doomguards) are there to keep monsters in. They're not going to fight the party, normally. If the players really search the room the triangular stone in the floor can be found, but no triggering mechanism exists, here. It's an automatic ball deflector, only rises after #16 is tripped. The grate door covering the short hall to #33 was hullmetal and locked before the wards were put on it. Designed to tease but tough enough to require a higher level to open. The pit is deep (hundreds of feet).
The doorway to hallway section #7 is Eldar Bronze but unlocked. There IS a key hidden on top of the lintel on the other side (inside). Make it nearly impossible to find.
Area #8 is a lot of fun. The panel on the left side of the hall is not easily found and has no local catch. It's part of the trap in #8. The trap door is under a large rug and not obvious (heavy minus to randomly find). I usually use the raising of either side sarcophagus lid as the trigger. The trap under the rug drops into a steep ramp, pulling the rug in. What makes this a real pain is the panel in the hall lifts and releases tons of mixed rocks that are stored in a steep chute. Note the elevation at the upper end. Those rocks blast out and sweep anyone in the doorway into the chute and down to area #39. Add in Arduin Krag Spiders as some of the rocks, undead rising from the 5 sarcophagus, 3 animated tomb guardian statues and whatever horror is living in areas #39 and #40. Guaranteed fun for all.
There's also a #8 further down the hall. I really should make them 8a and 8b. The 'Y' has a narrower arm to the left, stairs rising to a locked door of Eldar Bronze. The key should be somewhere deeper in the complex if you want to have fun. Otherwise, #12 is designed to be the classic temple room showdown. Big boss on the throne, two visible guardian statues on either side, two hidden behind fabulously valuable tapestries that are almost certain to get trashed. Pit trap in the room under a rug and six big statues holding up the roof make for a great fight. Swap out the rug with a heavy duty lurker or.... I usually have the boss escape out the priest hole behind the dais. What's NOT apparent is the actual escape is via a 1-shot teleport rune on top of a trap door. Except when opened the shaft to nowhere is full of spiders, wasps or whatever makes the players squeamish.
Area #19 is a false sarcophagus and an easily found secret door. Put something fun but mostly delaying in there, then let them figure out how to move the 1.5 ton sarcophagus away from the door. The door is held by several linked bolts, so an unlock or a disarm gets them all - and it's NOT a hard lock. Then the tons of fine dry sand in the steep shaft beyond start pouring out! Add hidden scorpions or sand snakes for more fun.
Area #16, Yep, pure Temple of Doom goodness. There's a pedestal in the mouth of a mucking huge carved stone face. Put something really spendy on the pedestal. Add lots of spells and cloaking magic. This is the classic, with a twist. The item is a solid illusion of what's on the pedestal in area #26. So, even if an equal weight item is swapped, removing the solid illusion from the pedestal triggers the big round ball at area #24 to start rolling. At rest it completely blocks opening the secret door from area #18 from either side. Down it comes with a bunch of lesser rocks behind. Have those bounce and catch anyone trying to cling to the top of the ball chute.
In classic fashion the ball rolls rapidly down through 8 and 7, the door to area #5 opens automatically and the now risen ball deflector sends the ball towards the entrance. That mysterious ridge blocks the ball from exiting and it bounces back to a rest across the entryway pit, mostly blocking the passage. Have fun getting out.
Area #26 is a deathtrap, an octagonal room with three high level golems guarding a four chest level treasure. The first time a party made it to the room, I'd set the golems to not activate unless the treasure was taken. I'd placed mithril golems, just to make it special. Believe it or not, the party managed to build a lightweight panel and fit a vertical 10x10 portable hole into the room. The golems ignored it as the players didn't touch the chests. They then managed to maneuver the panel around and tip all the golems into the portable hole intact. Yes, they managed Grand Theft Golem! Great role-play and creativity. Damn straight I'll use a different set of designs next time, but they earned the prize this time.
Lots of hidden areas are triggered by special items. I use large ornate keys, very clearly of an elemental focus. The passage from area #12 to area #20, entry to area #31, area #38, passage #25 are all solid rock with a brass keyhole. Insert key, turn and the rock opens into a shaped passage. The key and keyhole are usually to one side or another. Remove key, the rock reverts to filling the space. It's a fun trick, as there's no actual passage UNTIL the magic reasserts itself.
Options and notes
Make the traps hydraulically powered. Have something spring a leak and flood an area with slushy water. Area #21 leads down to a giant cavern with a lake... or something else if you want. The main pit cuts down to more levels or something best forgotten.
All doors and gratings are locked. Eldar Bronze is nearly as tough as durachrome or hullmetal, but is also enchanted. It's meant to be the magical equivalent of MDC (Mega Damage Capacity) items. Very few things should be able to harm it.
Make the whole area warded, so teleports and dimensional travel are blocked. This is the low security area where someone stashed folks they didn't want reanimating. The lower levels hold the really nasty stuff!