Hermit

A hermit is usually a religious person who decides to live a solitary life so they can contemplate their god without extraneous distraction.

Some hermits in earlier periods of the Christian church were immured into churches — i.e. were in rooms which were bricked up. ( was not a hermit, although in the same state.)

Not to be confused with hermit crabs, though some hermits can be quite crabby.