Underwater cavern.
In Pokemon Sapphire, you can capture Kyogre after encountering it once in the cave where you met Archie. Kyogre will flee to Sootopolis City and arrive in the Cave of Origin, north of Sootopolis City. You will need to trade for Kyogre from Pokemon Sapphire or Emerald to obtain it in Pokemon Ruby. In Pokemon Emerald, Kyogre can be found in Marine Cave when the guy at the Weather Institute announce bad weather in the sea.
Yes. Kyogre is the main legendary Pokemon in Sapphire.
It is in the cave where Archie of Team Aqua tries to capture Kyogre. Alas you need HM Dive to get there.
You can only get kyogre in sapphire you get it at the cave of origin.
kyogre does not evolve
You can't get Kyogre in Pokemon Ruby but you can get Kyogre in Pokemon emerald and sapphire and in ruby you only get groudon and rayquaza. In sapphire you get Kyogre and rayquaza and in emerald you can get groudon, Kyogre, and Rayquaza.
Kyogre!
Kyogre is available in Emerald and Sapphire but not in Ruby.
The Seafloor Cavern is in route 128, south of Mossdeep City. You need to use dive to access it.
You battle Kyogre for your chance to capture it in Pokemon Alpha Sapphire after you capture the groudon.
buy Pokemon Sapphire