One Piece: Umi no Heso no Daibouken-hen
English title: One Piece: Adventure in the Ocean's Navel
Japanese title: ワンピース ルフィ落下!秘境・海のヘソの大冒険
Type: TV Special
Episodes: 1
Source: Manga
Genres: Action, Adventure, Fantasy
Studios: Toei Animation
Duration: 49 min
Rating: PG-13 - Teens 13 or older

The Straw Hats encounter a city in the middle of a whirlpool, called the Ocean's Navel, that is being destroyed by giant monsters. These monsters supposedly protect a treasure capable of granting wishes, but in the process of defeating these guardians, the crew ends up releasing another evil. (aired after Episode 53)

(Source: Wikipedia)