I've said it here before, Spa World is a major gay hangout in the evenings, particularly on the weekends. On Saturday/Sunday morning, particularly during school breaks in nicer weather, it's a family venue packed with screaming kids and exhausted parents; after 6pm it's one of Osaka's premier hangouts for (likely closeted) gay men looking for a hook-up, or at least to inspect the goods. When I was living in Osaka I practically lived at SpaWorld during the campaign special seasons, but I went during the weekend lunch hours so I was completely unaware of the demographic shift once the sun went down; when I returned for visits in the years later and would pop in for an evening bath after arriving at KIX, particularly when I was govt property and had a govt property chiseled physique, I noticed dozens of creepy assholes giving me the stare-down and quickly caught on. And while I'm not queer I'm certainly vain so I enjoyed parading myself around letting a bunch of desperate closet queens catch their thrills.
If OP is of that persuasion, then Friday or Saturday night around 8pm to midnight should be quite engaging. The steam/sauna rooms on either 4F or 6F are well-suited and utilized action zones.
