Pokémon Ruby and Sapphire/Meteor Falls

Meteor Falls (Japanese: りゅうせいのたき Meteor Waterfall) is a large cave west of Fallarbor Town with a waterfall inside.

Meet Enemy Team
Team Magma or Team Aqua will steal a meteorite from Professor Cozmo at the Meteor Falls. Go straight north to receive a Full Heal. Then return to the starting point and head west across the bridge. There you will stumble upon Team Aqua/Magma. But as the Team is warning you, the opposite team walks up and tells them to stop. Afterwards, they will go to Mt. Chimney, while Professor Cozmo returns to Fallarbor Town. If you head south, down the stairs or slopes, it will lead to Route 115, which leads to Rustboro City. Right now, go back to the cable car on Route 112 which is now open. Come back after getting the Waterfall HM to explore more parts of the falls. You can then take the Dragon Claw TM and search near it for the rare Pokémon Bagon.

In Pokémon Emerald, Steven Stone also appears deep inside Meteor Falls after the Elite Four is defeated. His Pokémon are considerably stronger than the Champion's. Like several other graphical changes between Ruby and Sapphire and Pokémon Emerald, Meteor Falls completely changed color.

Return after obtaining Waterfall HM
Go up the Waterfall in the first room, surf, land and enter Room 2. Walk up and right to a ladder and go down to Room 3. Go down to a ladder and go down it. Back in the 1st room, you get an item. Go back to Room 3 but now go left. Go all the way up and down the ladder, back to Room 2.

Go right. There is a couple for a battle. Then go past and up by four steps. Go right and battle a boy. Below are slopes. Start jumping down, keeping left and take their left fork. After 6 slopes, walk left (Avoid slope 7 or you’ll be back to start} and go down the ladder back to Room 3.

Go down, then right. Surf right and up and land. Enter Room 4. This is a dead end, but there is TM02 Dragon Claw. There isn't anything else to this room.

Exit and use Surf, keep to the right and it will end in another doorway. This contains a PP Up in this area.