You must first go through the cave of origin.
The Cave of Origin is accessible through Sootopolis City.
Surf to Evergrand city through the victory road and defeat the Pokemon league
Sootopolis city.
pokemon snakewood is a hacked version
in sootopolis city
in sootopolis city
Sootopolis City
Sootopolis
sootopolis city
After you defeat the Mossdeep City gym leaders, you can either go to Sootopolis City or you can go to the Seafloor Cavern to defeat Team Magma. I would suggest going to Sootopolis City before you take on Team Magma so that once you've gotten through their hideout, you can just fly back to Sootopolis to capture the legendary pokemon.
Underwater around sootopolis city and mossdeep city
You have to fish at Sootopolis City.