On Cinnabar Island you can't really do anything. You can do 2 things, Heal your Pokemon at the Pokemon Center and meet Blue (Gary) the 8th gym leader of Kanto. Once you defeat Blain on the seafoam islands next to Cinnabar, You can battle Blue in Viridian, but only after you talk to him on Cinnabar
Find the secret key in the third floor of the burned down mansion (In which you just hit the switches on the statues to open the locked doors on each level to get there), and then once you find the secret key, fight Blane in the Gym.
But that's how you get the Badge.
But if your asking what you CAN do in Cinnibar, then I say you can evolve the fossils you get throughout the game in the Pokemon Lab. Its the last door down the hallway and talk to the guy in the right corner.
Or you can find some hidden items in the mansion with an itemfinder, which is what I like to do. Its fun finding items in cool places. I feel cool doing it. You know, its like finding treasure. Awesome. :)
But other than that, there's really not much.
Hope I helped! :)
you catch it at mt.ember in one island. you will be able to go to one island after defeating blaine, the gym leader of cinnabar island.
You will need to work your way to the basement in the Pokemon Mansion, you will then find the Key.
Its inside a pokeball inside the Pokemon mansion on Cinnabar Island
On cinnabar Island, to the left of the pokemon center, lies a "laboratory". If you go inside, then go to the right and enter the third door. Talk to the Professor there.
If you mean Pokemon FireRed/LeafGreen on the GBA, the mansion is in the top left corner of Cinnabar Island. (home of the seventh gym)
on cinnabar island
Cinnabar Island
there is no cinnabar island in sapphire. cinnabar is on firered and leafgreen. also in Pokemon yellow special pikachu edition ^_^ don't forget that dude...
Cinnabar Mansion on Cinnabar Island, that is, if you're playing FireRed/LeafGreen!
Cinnabar island use a great rod.
The 7th gymbadge is in Cinnabar Island
Cinnabar island
Surf from Cinnabar island left there you can get in.
Seafoam Island - East of Cinnabar Island - Southwest of Fuschia City
in the Pokemon mansion that is where than is on cinnabar island
you have to go inside the dungeon on that island and find the exit on the other side
Cinnabar Island where the burnt down Pokemon mansion is found is not available in Pokemon Emerald. This location is available in Pokemon FireRed and LeafGreen.