Unlocks the Builder ability to construct a Monastery.
+2 Faith, +1 Housing. +15 HP healing for friendly religious unit on this tile that has not attacked this turn. +2 Faith from every adjacent District, which becomes +3 Faith after progressing 'Reformed Church' Civic. Extra +1 Housing after progressing 'Colonialism' Civic. Cannot be built adjacenct to another Monastery. One per city.
Once Buttress is unlocked it can also be built on Floodplains.