Sapphire Sea

Sapphire Sea is a dungeon in Aurora region, located in Fantasy Bay. It's one of the dungeons containing HMs. This is the only dungeon rewards the players the HM Surf. The dungeon is found far north of Florea Town and you also can get to it by using Surf at the east point of Borealis City.

The dungeon is full of Water pokemon so it's good to train pokemon strong againist Water.