The hardest challenges in Pikmin 4 come from the dangerous areas and bosses within caves, dark underground zones that act like dungeons you must be prepared to explore. Although there are no time limits in caves like there are on surface maps, more enemies roam in the dark than in any other place. By carefully moving through different sublevels, you have a chance to find a ton of various treasures and resources.
https://screenrant.com/tips-before-exploring-caves-pikmin-4/