An airport built in the ocean, specifically Osaka Bay, is likely referring to Kansai International Airport.
Kansai International Airport (KIX) is built on an artificial island. As stated in the reference, it is located on an artificial island (Kankūjima (関空島)) in the middle of Osaka Bay off the Honshu shore, 38 km (24 mi) southwest of Ōsaka Station, and is situated within three municipalities: Izumisano (north), Sennan (south), and Tajiri (central), in Osaka Prefecture. This placement effectively positions the airport "in the ocean," or more accurately, on land reclaimed from the ocean.
