Sea Mauville (Japanese: シーキンセツSea Kinsetsu) is a decrepit research facility in the Hoenn region located to the north of Route 108. The second part of the structure can only be accessed by using Dive and contains the Scanner.
Sea Mauville includes both the decrepit platform itself as well as the water area and sandbar outside of the ship; the northern exterior can only be accessed by travelling underwater inside the platform using Dive.
In Omega Ruby, a portal appears at the end of the beam that extends a significant distance east and upwards from the platform if the player has the Clear Bell; interacting with this portal will initiate a battle with Ho-Oh. In Alpha Sapphire, a portal appears at control desk in the submerged control room if the player has the Tidal Bell; interacting with this portal will initiate a battle with Lugia.
After the Kyogre/Groudon incident, in the lower left room of the right side of the hull, when the player enters the room the message "It feels as though you're being watched" will be displayed. If the player examines the left section of the bookcase in the upper-lefthand corner of the room, they will find a blotched out report regarding the history of the facility, after reading which the same message appears. After this, if the player opens a menu such that they cannot see the overworld, upon returning the screen to display the overworld the Odd Keystone appears, enabling the player to battle Spiritomb.
History
Sea Mauville was a facility commissioned by Mauville City and led by Wattson to extract the natural resources of the ocean. Members of the staff included Captain Stern, Dock, and Professor Cozmo's father Raizoh. Due to several incidents, such as the closure of New Mauville, the facility was closed. After its closure, an environmental survey discovered that the ruins had created a unique habitat for Pokémon and plants, such as mangroves, which only grow there and in Mossdeep City. Because of this, its demolition was canceled, and the ruin was revived as a natural preserve.
Letters
Five letters, a photograph, and a drawing are found in the nearest room to the player after coming through the first underwater path:
First:
"Dear Daddy,
"How are you? Are you working really hard? I'm doing well. I'm doing all my homework, and I'm helping at home, too. Mommy's working hard and makes us dinner every night. Do you have to work this weekend? Are you going to come home? If you come home, take me to see the star show, OK?
"—Takao Cozmo
"P. S. I'm going to send you the picture I drew at the Trainers' School."
Second:
It looked like another letter, but it's a drawing. The drawing is of a boy's face, and written next to it are the words "I love you, Daddy."
Third:
"Dear Daddy,
"How are you? Are you working really hard? I was sad that you didn't come last weekend. But Mommy didn't seem so sad. She went out with her friend. I finally got that telescope that I've been wanting. It was from you, wasn't it? Thanks, Daddy. I really, really wanted it. I like looking at the sky, Daddy. When I look at the stars, I wonder if you are looking at the same stars, too. Let's look at the stars together, next time you come home.
"—Takao Cozmo"
Fourth:
"Dear Daddy,
"How are you? You aren't working too hard, are you? You never come home anymore. I'm worried if you're OK. Mommy goes out with her friends a lot. It seems like fun, so I guess she's doing OK. The Shelgon that you gave me evolved the other day. But I liked it better when it was a Shelgon and it looked like a Meteorite. Salamence was kind of a letdown, so I asked a friend to trade it for his Solrock. I'm sorry, Daddy. I know it was a present, but I think Solrock is cooler. When it gets dark tonight, I'm going to look at the stars again. I'll think of you when I do.
"—Takao Cozmo"
Fifth:
"Dear Daddy,
"I was really, really happy to get to meet you the other day. It was so fun playing together again and going to see the star show, too, even if it was just the two of us. It was sad that Mommy couldn't go, and even more sad when you and Mommy fought that night. I'll study hard, just like you told me, and I'll be a good boy, so don't fight. But let me keep watching the stars, even if I have to do all my homework, too. When I grow up, I want to be a professor and study the stars.
"—Takao Cozmo"
Sixth:
"Dear Daddy,
"Thank you for writing to me. I'm doing really well here, so please don't worry about me. I hope I'll see you again someday. I dream about it all the time. I brought the telescope you bought me to our new house. Please don't work too hard, Daddy. I hope you are OK. I will always, always love the stars, and I will always, always love you.
"—Takao Cozmo
"P. S. I'll give you my Hi Skitty doll. Please take care of it for me."
Seventh:
It looked like another letter, but it's a photo. There's a little boy holding a telescope, with a woman beside him, looking bored.
Items
Due to the rotation of the camera upon stepping on the platform from the southern exterior, the player needs to press left on the D-pad or circle pad to move north, with all other cardinal directions rotated accordingly. While the camera is not oriented this way while the player is in the southern exterior, it is while in the northern exterior.
Apart from the small sandbar which the player can land by Flying or soaring (which contains no items), Sea Mauville cannot be accessed without Surf, so all items located here require Surf to obtain.
Northwest (upper right) item ball in group of three in corner east of (below) TM13 (Ice Beam), accessed via the western (upper) pathway among the boxes
Southwest (upper left) item ball in group of three in corner east of (below) TM13 (Ice Beam), accessed via the western (upper) pathway among the boxes
Southeast (lower left) item ball in group of three in corner east of (below) TM13 (Ice Beam), accessed via the western (upper) pathway among the boxes
Southeast (lower left) of entrance, blocking one of the ways into the western (upper) pathway among the boxes
Northeast (lower right) item ball in group of three in the back of the eastern (lower) pathway among the boxes
Southeast (lower left) item ball in group of three in the back of the eastern (lower) pathway among the boxes
South (lower side) of the entrance, near the water
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.
Trainers with a PokéNav by their names will be registered in the Trainer's Eyes or Match Call function after the first battle, and may have a rematch with the player with higher-level Pokémon.