The Inferno is One-Eyed Willy's pirate ship. Willy and his band of pirates sailed it through all the seven seas back in the 1600s. Willy sealed the ship and it's crew within a cave to escape the British armada that had been sent after him.
Hundreds of years later, the Goonies find the ship still intact and seaworthy, along with the precious treasure and deceased crew aboard. When the Fratellis clumsily take some of the treasure they set off a booby trap that causes the cavern to collapse and frees the ship. The Inferno is last seen sailing adrift in the Pacific Ocean.
The filmmakers created a full-scale ship for the Inferno. The scene where the Goonies first see the ship was also the first time the child actors got a chance to see it, a trick that Richard Donner intended to provoke genuine surprise in the kids' performances. Unfortunately the ship was destroyed after shooting because they couldn't find anyone who wanted it...