I'll give you another example of the three-level solution.
Party was in a crypt
there had been an orcus cult near a High-elf city area a few millenia before. The cult had started turning a partly-completed crypt into an Orcus temple, but had been stopped before they got too, too far. (Cult started by taking advantage of a local leader's grief over death of their lover) To hide this shame, the local elves turned the orcus temple back into a crypt and sentenced the ringleaders to having their spirits be crypt guardians - being removed from the cycle of death/rebirth being the worst punishment possible.
The ring leader was left to starve in the inner crypt, but became an undead and had over millenia both gone completely insane and managed to tune his powers enough he could psychically contact a tribe of goblins who were doing his bidding.
The party's mission was to enter the crypt and stop this undead asshole; the party had already done the leg work to find out where the tomb was, that the undead asshole from long ago was likely behind everything, and he and his goblins were acting in the aid of an even Bigger big-bad and so he had to be stopped.
To justify the puzzle, the story was that the Elves confined the spirits to their coffins, but had to keep them sealed to complete construction work. There was also some hallowed dead in side crypts that they couldn't move, so they needed to have a mechanism to allow the spirits to be sealed so veneration rituals for the hallowed dead could be performed.
The spirits were also supposed discourage grave robbers and explorers - not to be immediately leathal face eaters.
The puzzle:
The party needed to solve an intentionally disabled teleportation circle. There were 6 missing runes in the teleportation circle.
There were 6 sarcophagi near by. Each houses a mummy that acts as a quasi-phalactery.
Once a living creature entered the chamber, after 1d4+4 turns and every 1d4 turns after, one of the mummies at random would spawn a Ghost (This was 4e so they were minions. Basically anything that'd go down quickly). If that mummy had spawned a ghost that was still active, or the mummy's ability to spawn ghosts was disabled, nothing would happen. I.e. the more of the puzzle the party solved, the easier it got to solve the rest.
The sarcophagi were in little mini-chapels detailing their lives via bas relief murals. There was a trader, an architect, a warrior, etc. There was also an inscription which was a riddle with solutions like a lantern, a coin, a knife, etc. The inscriptions could be detected to give off arcane and divine energies. There was also an indentation on the slab with the inscription (noticed with a low DC perception, or auto-noticed by anyone trained in perception who looked at the inscription).
If an item that the riddle indicated was placed in the indentation, the sarcophagi would stop spawning ghosts and an arcane specter would appear of the missing rune that needed to be carried to the teleportation circle.
The solution:
Correct solution: Solve the riddles, place the items on the coffins to stop ghosts from spawning. 3 of the items were in the room, 1 of them was a gold coin which the party had plenty of. One of the items (a quartz crystal) could be obtained by the party before entering the crypt, and there was a ' back up' copy in one of the adjacent rooms with the hallowed dead, but it was hidden behind another, more abstract riddle (the answer was "silence" - they had to do that and figure out it wanted them stop a fountain from flowing in a magically silenced room). 6th item was in the other room of Hallowed dead and was just there to grab.
The items also weren't random assignment: The trader's solution was a gold coin. The Warrior's was a blade. etc.
Lesser solutions:
The party could roll for INT checks to get hints on the riddles; only check per riddle per character, but there were three levels depending on how good they rolled.
Easy & medium, get a vague or a decent hint. Very hard, you just get the solution.
They could also channel divine energy with a medium difficulty to offline a coffin's ability to spawn more ghosts for a while. No penalty for failure. (The party never did this, and I didn't have a solid disable timer worked out, just a vague "should be turned off as long as they keep making process. Turn back on if they stall out or try to edge-case the puzzle" in my notes)
They could also do a very hard channeling of Arcane energy to try to make the ensorcellment on the inscription act as though the riddle had been solved. Failure causes an arcane backlash for damage and that coffin (or another coffin) to immediately spawn a ghost.
Brute Force/Mulligan:
The party, with a medium and then a very difficult Arcane check, could fudge one of the missing runes, potentially reducing the number of puzzles needing solved from 6 to 4 (or mummies being fought). None of the riddles were exactly brain boilers, but the idea is if the party has one riddle they are just not getting, they have a bypass.
The party could also smash open the sarcophagi - this would free the mummy which would then fight the party; defeating the mummy also released the rune. Mummies were difficult opponents than the ghosts (and could inflict mummyrot). This would make the Raven Queen and the Nature Gods a little miffed, as well really reduce the warm fuzzies the elves felt for the party.
But if you were stuck, its a way to proceed.
As a final back up, there was a returning goblin patrol that party could fight that had a scroll that would complete the circle. But unlike fixing the circle that would give them the option to come and go as they desired, using the scroll would be a one-way ticket. Better hope the boss has a way out and you can take him on.
Wrap up:
The party had the option of releasing the imprisoned cult leaders' souls (to face judgement in the afterlife), or leaving them to their fate. Releasing the souls got them points with the naturey gods for restoring them to the cycle. Keeping them imprisoned go you points with the more justicey gods for uploading the law. To make the choice harder, freeing them required depowering a unique magic weapon (and yes, coming back later was an option). I was a little surprised when they opted to free them.
Really it was more about seeing how their characters would respond (i.e. trolley problem) than anything mechanical.
