The Abstract Masterpiece is an item found in the GameCube title Pikmin 2. The item is in reality just a Snapple bottlecap, though the game's characters act as if it is a masterful piece of work, with the Dolphin (Captain Olimar's ship) explaining it as the "heart of art, the soul of creativity". It can be found in the Perplexing Pool's Shower Room (on level 6). It takes six Pikmin to carry the lid to the ship.
The "treasure" will give your team 30 pokos, the game's currency. This item and multiple others in the series suggest that the game takes place on Earth, though this hasn't been officially confirmed.