Pikmin: Spark/Dens

Dens are special subareas appearing in Pikmin: Spark. They are small caves appearing as holes in the sides of various structures in each of the five main areas. The appearance of a den's entrance is random each day. Dens contain a variety of items of interest that vary between each den. Some dens have a large number of enemies to grow Pikmin with while other dens might feature a small puzzle with a reward in the form of a rare piece of refuse.

To reach full completion and experience the true ending of the game, entering many dens is required as they contain unique refuse and exclusive enemies found nowhere else. While enemies are recorded in the creature log, the refuse is needed to access the true final boss.

Types of dens
Dens have a large variety of interiors due to being randomly generated like caves. However, the entrance of a den can be used to determine what the den's theme is. Some den entrances have two or more themes mixed into one to combine into a single special den.
 * Small: the den is small in size, being roughly larger than a standard landing site. Usually contains either many small enemies and refuse or either a few larger enemies or a single larger piece of refuse.
 * Medium: the den contains more complex terrain and hazards with a larger focus on elemental hazards and enemies. Contains a larger assortment of creatures and refuse.
 * Large: the den is the size of a small section of the main area, with a large variety of rooms and puzzles. This may contain a miniboss holding a rare piece of refuse.
 * Scratched: the den has a lot of enemies, and often enemies that are found exclusively in dens.
 * Flattened: contains a miniboss arena as the main focus of the den. Larger entrances can contain two at once.
 * Shiny: contains a large amount of Sparklium and refuse as well as enemies that can create Sparklium.
 * Underwater: only Blue Pikmin can enter it and features a large number of aquatic enemies and hazards.
 * Leafy: features a large amount of candypop buds, Pellet Posies, and plant-based enemies and hazards.
 * Sandy: contains enemies and hazards usually found in the Saltwater Glade.
 * Sooty: contains enemies and hazards usually found in the Cavern of Cobwebs.
 * Snowy: contains enemies and hazards usually found in the Chilling Frontier.
 * Grassy: contains enemies and hazards usually found in the Fertile Savanna.
 * Metallic: contains enemies and hazards usually found in the Rust Labyrinth.