tuto1 is an unused area in Pikmin. From the name and layout, it appears that initially, there were plans to have this area serve as a tutorial, linearly guiding the player through some of the game's concepts. Despite being extremely similar in name to tuto2, the two are radically different.
It is found under /dataDir/courses/test/tuto1.mod, and can be replaced by The Impact Site in Challenge Mode, in the European version, by using the following Action Replay code:
The only two textures in the entire area are checkerboard-like patterns with flowers on some of the squares, one of the textures having the squares green, the other yellow. Its geometry is quite simple, barred with walls steep enough for Olimar to not be able to cross them.
The area starts out at the beginning of a large path, on a small circular room. There are a handful of arches as the path continues, leading to another room, with some holes that lead very far down; once Olimar falls down, it's impossible to get back up. On the final room, there is a half completed bridge leading towards a raised circular platform.
The map starts at 7:27 in the video. Its geography was imposed on top of The Impact Site, which explains the weird object placement and the music.