Icefall Cave differs from the rest of the Sevii Islands since, rather than having a tropical climate, it is frigid and filled with icy caverns.
When the player first arrives at the cave, the only thing to do is to explore its inner first floor. Many ice tiles are scattered around, and if a tile is stepped over twice, the player will fall through to the floor below. There is also slippery ice in the inner basement floor, which causes the player to continuously slide in the same direction they stepped in until they hit an obstacle. By navigating through the inner cave's first and basement floors, players will find HM07 (Waterfall).
Once the player uses Waterfall to scale the waterfall to the back inner cave, Lorelei of the Elite Four will be found confronting Team Rocket Grunts. She will tell the player to help her defeat them, though the player only needs to confront one Grunt. After they are defeated, the Team Rocket Grunts will flee to their base on Five Island and Lorelei will temporarily stay in her house on Four Island.
The back cave appears to be connected to the ocean and is notable for being the only place to encounter wildLapras in all of Generation III. A woman in Four Island states that as a child, Lorelei met a Lapras here in Icefall Cave. Notably, she has one in her party.
While exploring the cave, they were attacked by a group of Pokémon. Before they could do anything, however, they were saved by Lorelei, who explained that Four Island is her hometown, and she wouldn't allow anyone to destroy it. The group was then ambushed by the Three Beasts of Team Rocket: Carr, Sird, and Orm. As they refused to give any information about Deoxys and the disappearance of Green's parents, an enraged Red charged at them, only to be narrowly saved from Carr's Forretress's Explosion (along with the rest of the group) by Lorelei's Slowking's Dig.
In the manga, it is explained that the cold temperatures in the cave are caused by the numerous Ice Pokémon living there.