From Bulbapedia, the community-driven Pokémon encyclopedia.
The Oceanic Museum is a building located in Slateport City. It plays a small role in the main storyline of Ruby, Sapphire, and Emerald. There are ten people inside the building. A sign outside the museum reads:
"The endless sea sustains all life."
OCEANIC MUSEUM
Structure
First floor
The player must pay an entrance fee of $50 as soon as they enter. After battling Team Aqua or Team Magma, the player obtains TM46 (Thief).
The first floor also contains information about the sea. There are seven exhibits, and a reporter who asks the player to tell him a story about Pokémon. This will later be aired on TV.
Second floor
On the second floor, the player will encounter more members of the villainous team. Additionally, this floor has nine exhibits, which include models of the Hoenn region and the ship S.S. Anne.
Trainers
Pokémon Ruby
Pokémon Sapphire
In the anime
Ash and his friends visit the Oceanic Museum in The Spheal of Approval and meet Captain Stern who is analyzing rock samples from the ocean's surface. During the episode, the museum gets attacked by Team Magma.
Trivia