One Piece: Karakuri Castle's Mecha Giant Soldier (2006) on Netflix

Plot summary

A storm at sea leaves a chest bobbing in the wreckage, and the Straw Hat Pirates pull it aboard to find Roba, an old woman, hiding inside. She wants to be taken home, and she offers the crew the golden crown she says is on her island, Mecha Island. No Log Pose points that way, so the pirates follow a Kame Pose instead, a small turtle that aims them at the island. The Going Merry has barely arrived when Dr. Rachet, the island's lord, attacks the ship. He then changes his plan for the intruders and asks the pirates to help him crack the Golden Crown's riddle, and the crew and his henchmen head into a cave on the island.