Anti-Stylites

Sort of shaped like this

I'll drop the in-game prose and just talk at you as a DM for this one.  I thought it would be cool to have religious hermits that, rather than living atop poles, lived down in holes.  Not caves-- think a bottle-shape carved from sandstone, the eremite living below with food lowered down and waste pulled out.

Now imagine a community of these holes close together.  They would probably do that to make it easier on the support folks.  Or maybe the support folks get inspired and carve out their own cells nearby.

  Now imagine all the support folk die of plague.  Or a war causes them to flee.  Plenty of creepy implications for our eremites.  Years later, players visit the valley/cave with all the hermit holes.  Some are filled with water.  Some have undead in them.  But all have a chance for holding holy items and texts.  Some might have mini libraries (no reason these hole dwellers need to be completely ascetic, maybe living underground is more symbolic).

You end up with something like B1's magic pools for players to investigate.  And I'm always interested in trying to put players in positions where they feel vulnerable as they explore-- like going down a hole alone.  Or, worse yet, submerging themselves in a water-filled hole.