Rest sublevel, also referred to as rest stop or rest level, is a general term used to describe sublevels in caves in Pikmin 2 that contain no or very few harmful enemies or other hazards, and large amounts of helpful items such as nectar, ultra-bitter- or ultra-spicy spray, or Candypop Buds. A somewhat common exception to the "harmless enemy only" rule is Doodlebugs, two Caustic Dweevils in one case, and Bulbmin found in another. Mamutas can also be found on some, but those help the Pikmin. They can, however, hurt the leaders.
A fair proportion of rest levels contain geysers, and they are most commonly found in long and difficult caves, often before or after sublevels containing boss enemies. Such levels usually contain large amounts of flora, Unmarked Spectralid swarms, Mitites, pipes which act as tunnels, and water low enough for any Pikmin to safely walk through. These areas can be identified by their calm musical theme.
If there is a Candypop Bud and the player has the need to have a full group of flower Pikmin, it's feasible to throw the Pikmin into the flower and wait for them to bloom. This is easy enough with any flower in any sublevel, but doing so above ground tends to be a huge waste of time.
Valley of Repose