There is a spot where you can dive south of pcificlog town. (Stay twards the bottom.)
no
the cave of regis is a place where you unlock 3 regi doors registeel, regice regiggis the other is in the sapharie zone
Type "How do you get the /three\ Regis?" because someone else has a long detailed answer on how to get to the underwater cave through to how to unlock the Regi doors so it isn't necessary for me to fully answer as he has. No worries :)
go to the seald chamber open the wall with dig. then you have to get relicant and a wailord. now read the dots on the wall and a earthqake will appear. now the cave that the regis are open
get all 3 regis and go the and the last regi will fight you
u have to unlock them by going in a certain cave. use dive and find a rock with braille writing on it and go in front of it then use dive again. then u do something in the cave and cause a massive earthquake that opens all the entrances to the regis.
you get regigigas by getting team charm to unlock the aegis cave the you have to spell ice rock and steel with the letter stones and battle the regis then you beat regigigas and go through the caves and spell again. (you might be able to recruit the regis on the way there) it is possible to get the king of the regis if you have luck but if not you have to go again Sorry but that is all i know:{
No because Regigigas appears in Regice's Cave and it needs to be caught or defeated prior to Regigigas appearing.
No. You have to transfer them from your emerald game. If you get all three Regis and transfer them over, you unlock regigigas. He is in the snowpoint temple. You have to get the national pokedex before you can do any of this.
it's not in dewford cave, it's in the sealed chamber.
get the regis all of them then transfer them to your game then registeel will have the key you do know the person is sped
it tells you how to unlock the regis