Gelatinous Polytope Maze
The collapsed building you are passing through looked like a small mountain of rubble from the outside but upon arrival you found a clean square tunnel running through the debris like a mine-shaft. The walls are an amalgam of wood, stone, plaster and other debris that has been fused into a smooth surface by whatever process cut the tunnel. The passage makes strange right angle turns in all directions; left and right, up and down. Underlying everything is a slight scent of vinegar.
For anyone with a passive perception of 15+:
The air in front of you wobbles slightly.
The party has wandered in to the lair of a gelatinous polytope. A gelatinous polytope is an hyper-dimensional version of a gelatinous cube. At the start of each of its turns it teleports adjacent to a random character and makes a Engulf attempt. On a successful save it still deals half damage to the target. When it teleports it brings all engulfed targets with it. If it takes enough damage to kill a gelatinous cube it disappears for one round before reappearing with full health.
Escaping the Maze
The party must escape the maze, to do they must succeed on 3 DC 15 Navigate Maze (Intelligence) checks to escape. All characters may spend their action to make this check but only accumulate one success per round. If any members of the group fail the check the group is faced with a minor obstacle a 10 foot wide 20 feet deep hole to a different section of the maze or a dead-end with a 10 foot climb. It is a DC 12 Athletics check as part of a move action to clear these obstacles.
If the party becomes separated (such as falling down a pit or failing to climb the wall) each group must make their Navigate Maze checks separately but keeps all success that were made already and obstacles only affect the group that triggers them.
Arcana DC 18 – To realize the hyperdimensional nature of their foe. Gives the party advantage on their next Navigate Maze roll.
Perception DC 15 – To reunite with the rest of the party after being separated.