An ancient box rumored to have been stashed away by an exploration team long ago, said to be bursting with gold, silver, and other treasure. It is worth an enormous amount of money! -In-game description
The Lost Loot is a rare item that can be sold for 4000 Poké. It has no other purpose besides this use. It may be found from prospect missions, in treasure boxes within Golden Chambers, and, very rarely, from crushed walls in dungeons.