The collection of islands near Cinawood City are refered to as Whirl Island. Although each piece of land seems to be its own island, they are all connected and exploring one will lead you through to all the rest. This is the island in which you can find Lugia if you have possession of the Silver Wing.
Apart from the legendary Pokemon of the sea, you will find here an array of Water and most likely Ground-type Pokemon. There are also a few items which are usually found in caves, but serve no real importance.
Cinawood City Pharmacy.
Route 45 is south of Blackthorn City.
It is located in Violet City where the first gym you encounter in the north of the city
go to vermlin city and surf with a blastoise
The 5th Gym is in Cianwood City in Pokemon Gold, Silver, and Crystal.
Outside the gym of CINAWOOD CITY there's a woman. Beat the gym and go talk to her, and she'll give your the HM FLY
Cinawood City.
in wrpl islands (down at city with lighthouse)
Cinawood city. Inside the pokemart which is blue most likely located in a city near a Pokemon center.
you have to surf from Olivine city, then you'll find your way through there.
After cinawood, you go back to ecruteak city then to the next city to the right from there, I believe.
Cinawood city, which is in the next town after the one with the lighthouse.
I have gold and silver, which almost is the same as crystal (the same generation). In those games, whirl islands is east of Cianwood City. You can go on the pokegear and look at the map. If you surf east from Cianwood City there are a couple islands there. It is hard to find whirl islands, but as you land on an island, look on the map and see if you are on whirl islands. If your not, try more islands. It is not that hard, but dont forget to have a pokemon with you that knows whirlpool.
Cinawood City Pharmacy.
not
In Goldenrod city, but only in the Japenese version of Pokemon Crystal.
You'll need the Silver Wing from Pewter City and go back to Whirl Islands and find it there. Recommend Flash and Surf.