I just thought of an EVIL dungeon.
Backstory: i work for a company that does vacation packages (I’m not a travel agent because im hourly with incentive not purely commission). One of the partner hotels gave THIS as a way to encourage us to book through them. It’s basically a six sided maze with pits where the ball gets stuck but the more i stared at the it the more i wanted to make it in a game.
So you’ll need one of these, that way you know your map is properly aligned. Photocopy it and trace it (to scale) onto grid paper. Let your adventurers go around on it.
The goal is to clear all the sides and get to be center. The pits i mentioned earlier are designed to get the ball stuck but i say make those lead to other sides like short cuts, and in doing so your players will see there is a portal to go through in the center they must find the right one. (They can’t go into the wrong hole see the portal and travel to it like by flying).
When they first begin they think it’s just a maze but when they get to the edge it looks like a cliff with canals cut into them vertically. As they attempt to scale down it it, the gravity shifts and they’re walking right side up. If they get to the hole and attempt to scale down it, same thing. If they throw something down the side it will land on the floor and reveal the gravity shift and the 3 dimensional nature of the maze.
Each side has some small villains, a mini boss (your discretion) and there’s a major boss blocking the portal in the center. “Find the path” and “guidance” doesn’t work, and you cant raise above the wall. Once they defeat a mini boss give them a hint which way to go so they can clear all six sides. Obviously give them some dead ends where they can rest and recover. This will REALLY aggravate your players but give them decent rewards along the way to keep them motivated, don’t skimp out on the magic items (if you don’t want to get too many magic items make them consumable magic items like spell scrolls and potions).
The maze is on a demiplane. Once they clear it and get to the center, perhaps they can use it as their own prison for future encounters.
Variant: if your players are god tier (in the 20 range) then maybe you can add a divine twist to it: those who know the Kobold legend know they constantly seek their god Kurtulmak who was trapped in an underground maze by the gnome god Garl Glittergold. But they’ve been digging for eons now and no sign of their god. Maybe that’s because Garl was a crafty gnome and didn’t hide Kurtulmak on the material plane but a demi Plane. Maybe your characters are in the same maze being chased by Kurtulmak and they must escape without freeing him.