Seems like as good a place as any to put in a request or two
I'm not actually
expecting anyone to make these, and would like to mention that anyone else following suit with posting some suggestions should keep in mind that actually creating the vaults are at the vault makers discretion (and implementation one step beyond, yadda yadda). If nothing else, maybe these will help give you some interesting ideas of your own.
Vault of the Octopus King. Central circular/oval room with 8 tentacles maybe? Kraken in the center with Octopodes running around throughout. Drop in 1-3 Unrand Octopus King items (between rings and trident) preferably. Should definitely have some water too.
Someone in another thread mentioned a vault where there is a dead adventurer with both the Singing Sword and gong shield. That would also be pretty cool.
Something similar to the L:1 entrance vault with all the monster behind glass, except the glass all disappears when you get a certain distance in. Maybe include something in the center that would make going in there worthwhile. Randart jewelry maybe? Would probably want the item visible from the entrance door, but inside a 'U' of translucent stone to prevent just apporting.
There have also been a few mentions of folks interested in a dead rising vault where you get surrounded by a zombie horde.