The Seagaia Ocean Dome (シーガイアオーシャンドーム, Shīgaia Ōshan Dōmu) was one of the world's largest indoor waterparks, located in Miyazaki, Japan.

The Polynesia-themed Ocean Dome, which was part of the Sheraton Seagaia Resort, with the world's biggest retractable roof, which was opened and closed according to the weather conditions;[1] 12,000 square metres of sandy beach, crushed from 600 tonnes of stones; an "ocean" six times larger than an Olympic pool, filled with 13,500 tonnes of unsalted, chlorinated water[1] kept hot at 28°C, equipped with a wave-machine with 200 variations, and listed in the Guinness World Records as the biggest simulated pool.

A 340 hectares (840 acres) resort, it boasts five hotels, several golf-courses, a botanical park and a zoo.

The Ocean Dome water park, which opened in 1993 along with the rest of the complex, was visited by 1.25 million people in the peak year of fiscal 1995.

Ripplewood had also invested an additional 3.5 billion yen ($32 million) on renovations for the dome; but even after the remodeling of the resort, the hotel closed down with liabilities of 276 billion yen ($2.5 million).