Solaniwa Onsen is a sprawling urban onsen theme park atop Osaka Bay Tower featuring nine different hot-spring baths—including outdoor, carbonated, silk, seasonal, and cold plunge baths—using mildly alkaline water sourced from 1,000 m underground. It also includes a 3,000 m² rooftop Japanese garden, private bath suites, saunas, and lively Edo-period village–style entertainment with festival games, dining, and relaxation zones.