From Bulbapedia, the community-driven Pokémon encyclopedia.
Dotted Hole is a place only accessible on Pokémon FireRed and LeafGreen. It is located in Ruin Valley on Fortune Island and is the place where players will get the Sapphire, which, in conjunction with the Ruby, allows Celio's Network Machine to connect to Lanette's PC system in Hoenn, and enables trades with Ruby, Sapphire, Emerald, Colosseum, and XD.
Along with the cave within Mt. Ember, this is one of only two locations in the Sevii Islands that has braille writing, both on the door, from which the area gets its name, and within, which will direct players to the location of the Sapphire.
Let the two glittering stones, one in red, one in blue, connect the past. Two friends sharing power open a window to a new world that glows. The next world waits for you.