Appendix:FireRed and LeafGreen walkthrough/Section 11

One Island Quest

Once you've defeated the Elite Four and obtained the National Dex from Proffessor Oak, Go back to One Island and talk to Celio, He'll tell you to go to Mt. Ember to get a mysterious Object.

Mt. Ember

Once you've returned to Mt. Ember, Go to the west side of the Mountain, you'll see two rocket gurnts, They'll open up a cave, Go in. In the cave you'll be able to capture some Slugma. You'll come to a room full of Braille messages about the Objects known as Gems. Continue on, and you'll find a room with a Red object that is the Ruby gem.Take it and return it to Celio, and he'll give you the Rainbow Pass which allows passage to Four, Five, Six and Seven Island.

Four Island

There is not much to do here, Except for exploring the cave known as Icefall Cave.

Icefall Cave

Here you can catch many Template:Type2 Pokémon, But deep inside the Cave you'll meet Lorelei a member of the Elite Four. She is there to protect a Lapras who has been Lorelei's friend ever since she was a child.

After you defeated Team Rocket, Why not explore more of the cave? After all, You might find HM07.