Slime Temple - one main dungeon with 4 sub dungeons in the surrounding area. The main dungeon is locked, requiring a key to enter. Each of the 4 sub dungeons is designed around one of the four elements, so water,wind,earth,fire. Initially though, the dungeon does not have access to the different slime elements, and so must acquire an elemental crystal to create elemental variants. To do this, each of the sub dungeons has an alter in the final room, which requires a elemental crystal to activate. Once activated, it allows the dungeon to absorb the crystal, unlocking an elemental slime variant. In exchange, it produces an elemental emblem. The alter can only be used once per dive, but subsequent activation's after the first can use elemental mana instead of a crystal, but produce a weaker emblem. The emblem's increase elemental magic attacks. All four emblems can be exchanged in the main dungeon to produce the dungeon key. True emblems will produce a key that can be used indefinitely, while weaker emblems produce a limited use key. (inspired from Slime Dungeon)
Twin dungeons - A single dungeon with a split core, one side becoming a celestial dungeon, the other infernal. Every x levels (5,10?) they share a joined floor, and the boss is some type of risen demon, fallen angel, or nephilim. Their first floor is a joined floor, with a large gate barring the way between. The gate key is found by defeating joined floor bosses, with each key only opening the gate for a set amount of time, or people. Lower levels yield better keys. The dungeon itself is situated inside a mountain range, with the first floor creating a safe passage through the mountains. Due to it's importance as a trade route, and the ambiguous nature of the dungeons, the church tolerates their presence, but individuals may launch personal crusades from time to time.
I have a few humorous ideas though; scorch that up with weird puzzle, and each of my bosses and demon lords.