The Great Deku Tree's Navel is a location from The Legend of Zelda: Breath of the Wild. It is located inside a knothole-like room in the Great Deku Tree at the Korok Forest in the Great Hyrule Forest region. This room is located under the Great Deku Tree's face.
It functions as an inn where Link can sleep on a Bed made of leaves, though unlike other inns the Korok innkeeper Pepp allows Link to rest here free of charge and refuses to be paid for his services if Link asks "How much?". Pepp reveals that he made the bed for especially for Link as he is Hylian Champion and the hero chosen by the Master Sword.
In addition to the Deku Tree's Navel Inn, the room also contains the Spore Store run by Natie and General Shoppe run by Daz. It should be noted that both the shops and inn share basically the same space inside of the Great Deku Tree with the Great Deku Tree's Navel being on the room's western side.
According to Natie, the room containing the Great Deku Tree's Navel Inn, Spore Store, and General Shoppe are actually located in the Great Deku Tree's stomach, which ironically also contains cooking pot in the middle of the room. A Soup Ladle can be found near the General Shoppe. The inn and room contains several acorn-shaped Pots which can be broken to occasionally find Acorns or Chickaloo Tree Nuts.
Maca reveals room inside the Great Deku Tree's stomach was decked out in anticipation of Link's arrival, giving him a place to rest and shop. The Great Deku Tree does not seem to mind this though, however Maca thinks that the Great Deku Tree probably isn't very happy about becoming a tourist trap.
Presumably the inn was named Great Deku Tree's Navel in reference to its location in the Great Deku Tree's stomach, as one's stomach and navel are located in the same area of the body. It may also be a play on the terms "Inn" and "Innie" (a slang term for a concave navel).