Grand Sea (Japanese: おおきな うみ Grand Sea) is a dungeon in Pokémon Mystery Dungeon: Red Rescue Team and Blue Rescue Team that contains 30 floors. It is automatically unlocked on purchasing the Serene Sea Friend Area, available after the completion of the main story. HM Dive is required to enter the dungeon.
The DeepSeaTooth can be found on 15F and the DeepSeaScale can be found on 25F, surrounded by water. If player already has them, they will be replaced by Link Cables.
Note: The % are rough estimates.