海遊館
Also known as Kaiyukan
Both vloggers rank this one of the best aquariums they've seen. The layout is the trick — you ride an elevator to the top and spiral down around a central tank holding whale sharks, manta rays, and giant Japanese spider crabs, so you keep re-meeting the same animals at different depths. Tickets around 2,700 yen for adults; grab them online to skip the queue.
Buy tickets ahead online. · Pair with lunch next door at Naniwa Kuishinbo Yokocho in Tempozan Marketplace.