This is a spoiler-free summary visible to all players. Fill in what any character would reasonably know about this location.
The Divine Realm is the plane where the Fragments (Deities) came from and where they retreated after their task in Arda was done. It is said that it's their home. Whenever lesser fragments tried to explain that place to humanoids, it sounded incomprehensible to mortals and languages lacked the vocabulary to describe it.