The Lost Islands are a pair of islands located of the shore of Port Decca. You can buy a ticket by going into a building and talking to the woman and you can buy a ticket.After purchasing the ticket, you can go to the Lost Islands by talking to a man that looks like a pirate on the right dock.There are Z-Crystals which allow your Pokemon to use their Z-moves.You can only use one Z-move per battle.There is a boat that is broken and says Tess if you keep on going left from where you start.You need a Z-Crystal pouch to get the Z-Crystals. You obtain the Z-crystal pouch from the Lady at the tent that are researching.If you don't have a Z-Crystal pouch and you try getting one it will say the crystal is radiating energy.The water Z-Crystal is obtained by using Surf and going between the island.The fire Z-crystal requires using Rock Climb and following the path the grass one is obtained by walking/running/using your overboard up the hill.
The Lost Islands are a representation of the Alolan region of Pokemon Sun and Pokemon Moon. This means that some Pokemon that are native to the Alolan regions may be found here. You can also evolve some Kanto Pokemon at the Lost Island into their Alolan forms. Only 3 Pokemon are known to evolve into their Alolan forms here: Exeggcute, Pikachu and Cubone.