Go to Lilycove city. Walk up the stairs by the pokecenter. Go to the right and jump down the ledges. Go down the stairs to the beach and use surf. Surf to the north and you will see the entrance.
I don't think you can get back into it once it's closed.
You can't. If you missed out on the Master Ball, you can't go back and get it. Ever.
It depends on what land you are in. In Pokemon Sapphire, you have to look east of Lilycove. In Pokemon Emerald it is in a different location. It has something to do with Mt. Pyre.
you battle them
near team aquas hideout in sapphire. but in emerald it is on MT. chimeny
it is in pacifidlog town i think
there hideout is by lilycove city and it closes up in end of game:)
You have to beat team aquas leader. His red orb will glow and kyogre will wake up.
A rock in the front is a good hideout to pass em
lilycove city or something like that
you go to modseep and vs the gym
team aquas hideout in lilycove
look up walkthroughs on youtube
Go to Slateport City, go to the boat port and after the cutscene, the hideout will be accessible.
Team Aquas underwater hideout is located in Mossdeep. You will need to dive down in the water and on the right hand side there will be a cave, which will be the hideout.