This Article Contains information directly from the Pikmin Games. This article is based off of an Enemy/Treasure/Area/Cave/Pikmin/Character from the Pikmin series of Games.
The Secret Safe is the last ship part that can be retrieved in Pikmin. However, it is not necessarily a part, because it has no purpose in making the Dolphin function. It apparently is a large safe, obviously shaped like a pig, better known as a piggy bank. This is where Captain Olimar keeps all of his money, or Pokos. When he found it, none of his Pokos were lost.
Collecting the PartEditStart building the bridge using 80 Blue Pikmin and then throw 10 Yellow Pikmin from island to island on the right side of the map. Once they have bomb rocks, throw them back the same way (if playing the Gamecube version, be sure not to whistle to them or they will drop their bombs-- you need to touch them! This was altered in the New Play Control release for the Wii). Take the bomb rocks across the newly-created bridge and use them to destroy the brick wall. Set aside any pikmin still holding bomb rocks and use both the Yellow and Blue Pikmin to start building the second stick bridge.
Take out 10 Red Pikmin and throw them onto the fire geyser ledge to the left. Then move into the water on the right side of the ledge, whistle to them, and lead them down to where the box is blocking the path. Use them to push the box while the Blue and Yellow Pikmin continue to build the bridge. Once the box is moved and the bridge is built, take down the white wall (perferably with a single bomb rock).