The entire Namba complex is like a labyrinth both above and underground. Not only do you find "the usual" but there are also the odd specialty areas as well (like the section just for those in the restaurant trade.... fancy a set of those japanese curtains "noren" that are over all the restaurant doors?) A trip to Osaka is not complete without a few hours wandering around in Namba. The toilets are all downstairs in the train stations and connecting passageways.
Easiest access via subway... several lines have stops there.