Instructions
Select Pokemon with the surf and whirlpool abilities for your team, as you need these qualities to access the Whirl Islands.
Head to Olivine City and turn left onto Route 40. Use surf to get to Route 41 and then surf to the island on the upper right. Use whirlpool to pass this location and find a cave entrance.
Move to the right once in the cave, leaping off a series of ledges. When the road forks take the upper path. You will eventually reach a ladder, which you should take down.
Follow the path at the bottom of the ladder until you reach a second ladder. Crawl down this ladder.
Move left down the path and speak to a monk. Show him your silver feather and he will let you continue. Follow a slope down to reach the entrance to another cave.
Speak to the Kimono Girls in this room. They will ring the tidal bell and do a dance. This draws out Lugia, who will battle your team.
Use a master ball, if you have one, to weaken Lugia. Sleep and paralyze are also good spells to use on this foe. Lugia has a high catch rate so you may have to use several ultra balls to capture it.