Adapted from one of the best dungeons I've ever come up with and run:
The entrance is marked "You will never find what you are looking for". Ideally, the players believe some macguffin is deep inside.
Inside the entrance, the walls are unadorned, solid, black. There are no lights. It is pitch black inside, and whatever lights the players bring don't seem to illuminate as much as they should. It's also freezing cold. It quickly becomes a maze of hallways, rooms, stairways, and intersections of all the same cold, black. They may find the frozen remains of previous adventurers that entered. They don't look like they died from violence. Just exposure to the cold, and maybe starvation.
Have the players map it themselves, and slowly make the layout make less sense. Have hallways loop back into what should be another room. Turn around to go back to the big room, and they find a small round room instead. And always the freezing cold gnaws at them.
The mechanic is
spoiler
You will, literally, never find what you are looking for. If you are looking for the treasure, you'll find endless rooms and halls instead.
This rule has more fun side effects. If the players decide to turn around and go back to the exit, they won't find it.
If the players split up, and then decide to regroup? They can't find each other
Leave tokens behind to mark your path? They'll disappear.
In my game when I ran this, they found a very large spiral staircase that went down farther than they could see. They spent some time walking down, looking for the bottom, and of course they didn't find it. They decided to turn around and go back up, but per the rules of this place they didn't find it. One of the players said "Fuck it. I have feather fall. Let's jump." They fell for so long, and it wasn't until their goal changed of "let's see if we can grab a landing??" that the bottom appeared.
The other clue my players got was they found a survivor from the antagonist's party that had gone ahead of them, and he said that the antagonist had just spent the whole time asking them a lot of personal questions. Where did you grow up? Where did you learn to read? What was your favorite toy? The trick there was to distract them from the actual dungeon, so they would walk without seeking anything.
If the characters walk without looking for anything in particular, it will cycle through a bunch of rooms and eventually take them to the heart.
(Yes, this was heavily inspired by House of Leaves)
The players had a blast with it. I was so proud of them that they figured it out.