Skypiea

The Straw Hats sail to a legendary island in the sky — Skypiea, 10,000 meters above the sea. This island was once part of Jaya in the Blue Sea, blasted into the sky 400 years ago by the Knock Up Stream. They discover an ancient civilization, the Shandians, who have been fighting for 400 years to reclaim their homeland from the self-proclaimed God Enel — a terrifyingly powerful user of the Goro Goro no Mi (lightning). Enel can hear everything on the island and kill with thunderbolts, making him seemingly invincible. But rubber doesn't conduct electricity — making Luffy his natural enemy. The arc explores the meaning of history, the Poneglyph, and introduces the idea that Roger could 'hear the voice of all things'. The golden bell rings again after 400 years, proving to the world that the City of Gold exists in the sky.