Valheim Serpent spawn locations
Serpents are giant sea creatures that spawn in the Ocean biome. They are currently the only hostile sea creature in the game, and they will readily attack both players and their boats of choice - even the mighty Longship.
There is no sure way to track down a Serpent because their spawns are completely random within the Ocean biome. Your best bet is to head far enough away from the coasts to get into the Ocean biome, but not to stray too much further into open sea, because you might want to return to the coast in a hurry once you've found your Serpent.