After you learn Sea Skim and Strong Push in Fuchsia City, you can explore the Seafoam Islands, where you can find a rare pokémon.
From the East
Read this section if you reached the Seafoam Islands from the east, by going south from Fuchsia City. If you reached the islands from the west, skip to From the West on this page.
Seafoam Islands 1F
Go east from the entrance until you can't go farther east. Then check the rocks to the south to find a hidden Heart Scale.
Go north from there and check on the tall stone block to use Strong Push (learned in Fuchsia City). Push the stone block into the hole on the right.
Go south, then go west from the Picnicker, then go north up the ramp. There is an Ice Heal to the left of the ramp.
Go north and you can battle Coach Trainer Yas, who has a level 46 Jolteon, a level 47 Flareon, and a level 46 Vaporeon. You get 4600 Pokédollars for winning. After the battle, you get 5 Rare Candies.
There is a ladder east of the Coach Trainer. Go down that ladder.
Seafoam Islands B1F
Go south down the ramp, then go east, then go north up the ramp. To the left, there is a Super Repel.
Go north past the ladder, then go east, then go south down the ramp. Push the tall block into the hole.
Southeast of the hole, check the rocks to find a hidden Max Revive.
Then fall into the hole that you pushed the rock into.
Seafoam Islands B2F
Push the rock into the hole.
Then go west and you will see a ladder. Before you go up the ladder, go southwest and check the rocks to find a hidden Heart Scale. Then go northeast and go up the ladder.
Seafoam Islands B1F, part 2
East of the ladder, there is a Max Potion.
If you arrived in Seafoam Islands from the west (via Cinnabar Island), then go south, then east, then north up the ramp and go up the ladder, then skip to the next "Seafoam Islands 1F" section.
Otherwise, go southwest from the ladder, then south, then when you can't go farther south, go east. Keep going east until you reach a wall, then go north up the ramp. Keep going north to find a ladder. Otherwise, go down the ladder. (If it's a ladder going up, you need to go south, then east, then north to reach the ladder that is going down).
Seafoam Islands B2F, part 2
Go southwest from the ladder, and go down the ramp. Ignore the ladder here, but go southwest from that ladder to find a hidden Heart Scale.
Go east from there to find TM55 Ice Beam.
Go east from there and check the rocks southwest of the ladder to find a hidden Pearl.
Then go north up the ramp, then go northwest and go up the ladder.
Seafoam Islands B1F, part 3
Go south, and go down the ramp, then go west, then go north up the ramp, and go up the ladder.
Seafoam Islands 1F, part 2
Go east to find an Escape Rope.
Farther east, you can talk to the guy to get more Poké Balls if you run out.
Go south down the ramp, then east, then push the tall block up or down once. Then push it to the left until it is next to the hole, then push it into the hole.
Go north and check the rocks north of the ladder to find a hidden Heart Scale.
Then go down the ladder or fall down the hole.
Seafoam Islands B1F, part 4
South of the ladder, there is a set of 5 Great Balls.
Push the tall block into the hole, then fall into the hole.
Seafoam Islands B2F, part 3
Push the stone into the hole.
Check the rocks east of the hole to find a hidden Heart Scale.
Go north and go down the ladder.
Seafoam Islands B3F
To the right, there is a Super Repel.
Go down the ladder.
Seafoam Islands B4F
If you arrived in Seafoam Islands from the west (via Cinnabar Island), then go west and go up the ladder, then skip to the next section ("Seafoam Islands B3F"). Otherwise, go south down the ramp. Go west to find a Big Pearl, then go east and check on the rocks to find a hidden Pretty Wing.
Go north up the ramp, then go west, and you will see a ladder. South of that ladder, there is a Big Pearl. Go north and go up the ladder.
Seafoam Islands B3F, part 2
Go north to find a Super Lure.
Then go west, then south. There is an X Speed to the left of a ladder. Check the rocks north of that to find a hidden Revive.
If you reached the Seafoam Islands from the east (via Fuchsia City), go to the next paragraph. If you reached Seafoam Islands from the west (via Cinnabar Island), you can go east from here and get the Hyper Potion east of the ramp, then go down the ramp. Then skip ahead to the paragraph that starts: "Go down the ramp, then go west. There are two stones side by side..."
If you reached Seafoam Islands from the east (via Fuchsia City), then go east from here until you see water to the east. Go north, then go down the ramp toward the water. You should be able to see the two stone blocks in the water, blocking the fast current. (If not, go up ladders to reach the first floor, then start at the beginning of the walkthrough on this page.)
Go south and surf in the water, then go east and get out of the water on the other side. Go north up the ramp and get the nearby set of 3 Ultra Balls.
Then go east, then south. Go up the ladder.
Seafoam Islands B2F, part 4
To the northwest, there is an Ice Stone.
Go east and up the ladder.
Seafoam Islands B1F, part 5
To the west, there is a Super Lure.
You can go south and go up the ladder if you want to leave the cave. This will take you to the western part of Route 20, which leads to Cinnabar Island.
If you didn't leave the cave, go down ladders from here until there are no more ladders to go down.
Seafoam Islands B3F, part 3
Go north and get into the water. Go west in the water, then get out of the water on the other side.
Go north up the ramp, then go west, then south, then east. There is a Hyper Potion east of the ramp.
Go down the ramp, then go west. There are two stones side by side that you can push. Push the rightmost block up twice. Then push the leftmost block down twice, then push it to the left until it is next to the hole. Go to the left side of the two blocks that are next to each other, and push the upper block to the right. Then push the lower block south into the hole.
Then go west and push the other block into the hole.
Then fall into either one of the holes.
Seafoam Islands B4F, part 2
Go northwest until you see a place where you can get out of the water. Get out of the water there, and get the Big Pearl near the left side of the ledge.
Save the game, then go north, and check on Articuno. Defeat it within the time limit for a chance to catch it. Use Ultra Balls (it is not recommended to use a Master Ball) and Razz Berries to help improve your chance of catching it. If you don't defeat Articuno in time, or if Articuno runs away while you are trying to catch it, you have to defeat the Elite Four to make it come back. (Or you can just close the game without saving, and try again.)
From the West
Read this section if you reached the Seafoam Islands from the west, by going east from Cinnabar Island. If you reached the islands from the east, go back up to From the East on this page.
Seafoam Islands 1F (from west)
Go down the ladder.
Seafoam Islands B1F (from west)
Go northwest to find a Super Lure. Then go east and down the ladder.
Seafoam Islands B2F (from west)
There is an Ice Stone to the left of the ladder. Go south and down the ladder.
Seafoam Islands B3F (from west)
Go north, then west, to find a set of 3 Ultra Balls. Then check on the water to get in. You will be pushed to B4F.
Seafoam Islands B4F (from west)
Surf north and get out of the water. To the left, there is a Big Pearl. To the right, check the rocks to find a hidden Pretty Wing.
Go north, and ignore the ladder for now.
Go west, then southwest, and you will see a ladder. South of the ladder, there is a Big Pearl. Go north from there and go up the ladder.
Seafoam Islands B3F (from west, part 2)
Go north to find a Super Lure. Then go west, then south, to find an X Speed next to the ladder. Check the rocks near there to find a hidden Revive. Then go up the ladder.
Seafoam Islands B2F (from west, part 2)
Go southwest from the ladder and check the rocks to find a hidden Heart Scale.
Go east from there to find TM55 Ice Beam.
Go east from there and check the rocks southwest of the ladder to find a hidden Pearl.
Then go north up the ramp, then go northwest and go up the ladder.
Seafoam Islands B1F (from west, part 2)
Go southwest to find a Super Repel.
Then go south down the ramp, then west, then north up the ramp, and go up the ladder.
Seafoam Islands 1F (from west, part 2)
Go southwest to find an Ice Heal.
Then go south down the ramp, then go southwest and temporarily leave the cave. There is a woman to the left of the cave entrance who will heal your pokémon.
Go back into the cave, then go up to From the East on this page to continue the walkthrough.
Moving On
You can go east from Cerulean City and surf in the water in Route 10 to reach the Power Plant, an optional area with a rare pokémon at the end.
You can surf in the water in Pallet Town and go south from there through Route 21 to reach Cinnabar Island, where the next Pokémon Gym awaits.