It think some subdungeons are universal, and some are tied to a direction. I also think the tileset is often a clue if some subdungeon only spawns in a certain direction (allthough I could be mistaken). Also, it's possible some only spawn depending on how far in a certain direction you go (but that I'm highly unsure of).
Ones I'm kinda sure of:
El potion loco (one with the mages, an experimental wand and a goblin which can net you a load of potions)
Goblin mines (5X5 with 3 pink goblin mines)
Pendragon (A purple dragon which gives you a Pissorff and some info)
Draco (Draco's heart, but you have to move a dragon out of the way)
Cha'Dylan (A large one with exploration and a guy in the middle of it who you can only Wonnafyt to yourself, drops a sensation stone)
Tree of knowlegde (a druid who sells various XP perks)
Spider temple (large one with toxic exploration and lots of goodies)
Contemplate the waters (a monk who sells a Lemisi for 25 gold and there's unreachable exploration)
Vegetarian Vampire (a puzzle minigame with plants where you can get small bonuses)
One with 5 plants which leave +5% damage charms (I think)
One with the +15% damage sword which you can't convert
I just now noticed that this wasn't what you were asking about (facepalm). So sorry.
I almost got pwned by Shifty Brickwork!