After you beat the Cinnabar Island's Gym, Bill will be waiting outside waiting for you. He will ask you to come with him to visit a friend. You can select yes and do that adventure now or no and do it later, it's your choice. Also, even if you decide not to, Bill will still be waiting there, so you can always have a second chance.
This is the 1st island and one of the biggest.
It has a larger Pokemon Center that has a system that allows you to trade with Ruby, Sapphire, Emerald and Colosseum. You have to power it with the Ruby and Sapphire plates first though.
It has a beach south of the Pokemon Center that has wild Pokemon such as Fearow in it.
After you do some stuff on the islands you can go up Mt Ember and catch Moltres.
After you beat the Elite 4 and get the National Dex you can fight two Rocket goons and enter a cave that has some wild Slugmas, some braille text and the Ruby Plate.
Two Island is much smaller and is like a village.
After saving a girl from a Hypno, you can enter a house and you get to play some mini-games with other people that have FireRed or LeafGreen.
Also at the top of the Island is an old lady that will teach your starter a special move once.
Three Island is manly a resort for Pokemon with it's ups and like, no downs.
At the east their is a forest with a girl that is under attack by a Hypno. You have to save her to get back to Cinnibar!
After you get the National Dex, you can go into the cave at the beach and at the end their will be a patch of grass full of Dunsparce.
In the cave you can get HM07 (Waterfall).
It has a Rocket Warehouse but you can only get in when you do stuff on Six Island.
Inside is a maze and Lot's of Rocket trainers and the guy who stole the Sapphire Plate.
At the top is a cave that has lots of items and is a maze.
Around the North-East is a man that gives you the Togepi Egg.
There is a forest up the top with a few battlers in it.
Their are some Ruins to the south that hold the Sapphire Plate that gets stolen by a Rocket guy.
To the north is the Battle Tower.
There is a strength puzzle that needs completing
There is 7 Ruins that have Unown in them but only found if you complete the Puzzle.
