In my current campaign I've introduced an island that is littered with the ruins of an ancient civilization. The island is always covered by dark clouds, and surrounded by bad weather, because the God of Storms is angry with its former people (The God of Storms holds a very long grudge). His lightning bolts are constantly striking the ruins of the temples, because at some point in time the tribe on the island started worshiping another deity. An evil deity.
This actually leads to a very interesting situation on the island, where minions of this evil deity can only walk around at night, under cover of darkness, so the God of Storms does not see them. There are these massive animated statues as well, that only animate at night. And the Watoto (the wandering undead tribe that was cursed for their devotion to this evil god), hide away during the day, but come out at night. The players can see their many spooky torches in the jungle during nightly hours, as they continue to do their evil god's bidding.
So it's not just a bunch of lore, but it also has an active effect on the gameplay. I keep the exact details a secret, so that as the players explore the ruins, they learn more and more about the fate of the tribe and how they were deceived by the evil deity.