The Darkness Within
Religion in this realm is diverse and active. Temples and shrines can be found in many places to innumerable deities. Gods are fickle: Sometimes they will take an active interest, sometimes they will ignore pleas. Sometimes they show up…
In game terms, any deity with a WotC writeup is worshiped somewhere, exists, and can be followed by PCs. Just make sure the DM can see a copy of the writeup.