Cave
Caves are areas in the game, Pikmin 2. In Pikmin 2, although there is a large overworld, most treasures are found in these caves, so you will be spending most of your playing time in caves. All enemies including bosses respawn if you return to a cave. The only exception to this seen so far is the 3 purple candypop flowers in Emergence Cave, this is to stop the player from easily gathering large numbers of Purple Pikmin.
Entering caves
The holes through which you enter the caves are round, rocky mounds, with a small hole in them with wisps of smoke coming out. Simply press (A) to enter it. Any Pikmin under your control will jump down with you, and any that are idle or working will return safely to their Onions.
Sublevels
The caves are split into several sublevels. The shortest cave has two sublevels; the longest has fifteen! Each sublevel usually has at least one treasure for you to find, and almost always one or more enemies. There are three types of sublevels. Every time you enter a sublevel, the game will save. So if you turn the game off then back on, you'll start over in the current sublevel you are on.
Normal levels usually have a few harmful enemies, and sometimes don't have any treasure.
Rest levels either lack enemies or only have harmless enemies. A somewhat common exception to the "harmless enemy" rule is Doodlebugs or, in one case, Bulbmin. Rest levels have Pikmin-supporting items, such as nectar, Ultra-Bitter Spray, Ultra-spicy spray, or Candypop Buds.
Boss levels are usually the final level of a cave. The only cave without a boss level is Emergence Cave, and the one with the most is Hole of Heroes. They hold one large boss enemy, and maybe a few normal enemies, and this enemy, when defeated, often drops an item which upgrades Olimar/Louie's space suit or ship.