PNF-404 - the Koppai designation for the series' central planet, and a pun on "Planet Not Found" - is roughly 70% water and implied to be a future Earth. It is the world of Pikmin 1 and Pikmin 2, not the Garden of Hope from Pikmin 3. The game opens in a cave hub and then fans out into six main areas, each with its own daylight cycle and its own set of caves.
This is the biggest structural change from Pikmin 3. Caves are no longer procedurally generated - every one is hand-designed, which means every cave has a fixed layout and a fixed solution. Floors are themed around dirt, metal and shed interiors, and muddy brick. Slow-moving floor fans replace the geysers of earlier games, and the whole cave runs at one-sixth speed. Because layouts are fixed, speedruns and guides can be exact, and because they are designed rather than generated, they tend to sequence their puzzles deliberately.
Caves include Burrow of Beginnings, Crackling Cauldron, Industrial Maze, Secluded Courtyard, Below-Grade Discotheque, Sightless Passage, Last-Frost Cavern, Hectic Hollows, Aquiferous Summit, Subzero Sauna, Doppelganger's Den, Drafty Gallery, Frozen Inferno, Cavern for a King (the final boss cave), Cradle of the Beast, Kingdom of Beasts, Plunder Palace, Dream Home, The Mud Pit, Ultimate Testing Range, Engulfed Castle, Seafloor Resort and Subterranean Swarm. Depth of Quarity is a late-game area as well.
Sparklium is the currency hidden around every area and cave. It is used to repair and power the S.S. Shepherd, the Rescue Corps ship, and to unlock progression. Because it is scattered rather than farmed, a first run is a scouting trip and a second run is a collection sweep - and the Switch 2 Edition's Dandori Academy exams turn that collection loop into a scored, repeatable activity.