Bathhouse lore! Bathhouse lore! Bathhouse lore!
when Heavengrounds was built after the realm-fall phase of the Universe being unstable, the first function of the place was to create a bridgeway to connect to the Bathhouse
the purpose of the Bathhouse is to protect those who want to traverse outside of their realm/dimension from getting their own existence unstable to the point of being destroyed
being cleansed by the water makes you invisible and practically non-existent to the Universe for certain amount of time, preventing from being infected with destabilization
post-Heavengrounds, the Bathhouse is mostly used by the angels as they don't originate from the mortal realm but before that, usually you'd find gods, dimension-hoppers, and other immortals --demons originate from the mortal realm, so they don't use the Bathhouse unless for travel
due to incidents of travellers coming back with slight destabilization from incomplete bathing (mortals typically not comprehending the importance of the water), the angels that are regulars there began to do monitoring work. most divines that work there are mostly voluntary.
Aro wears a 4-point star gem (which can be found on anyone only wearing the Bathhouse's module) that was given/made before a proper open bridgeway to the the place was built. it allows them to create a direct portal to any location within the Bathhouse. only less than a hundred are still used and functioning.
below the Bathhouse are the 'Spirit Waters' which was desire-pathed by lost ghosts and other spirit based creatures