Go explore the water cave on the souther tip. Hard to see cuz it's flush with the water. If u fly from the ruins with the stairs tht go into the mountain and had the natural farm to the main island Ull see it at night.
If you have a chance check out the ice cave in spectator mode on single player. Its the biggest cave system I've ever seen. There's a section where's there's a bunch of frozen dinos including a megapithecus. And even a sleeping Giga in an area.
its dark af u cant see a thing with out light source and even then its hard to see and the water u swim through is the same there are alot of enemies down there to