We just got back from German, Austria & Switzerland Tour. I just wanted to pass along a heads up about the Baths of Caracalla's view on appropriate swimsuits.
Women are expected to wear a one peace or bikini.
My wife had a two piece swimsuit similar to a burkini. It covered over her knees and draped across her middle. She was not allowed to swim. It covered too much. While there is no posting on the companies website about appropriate attire, that style swimsuit is not allowed. Sadly the shops had all closed by the time they told us this and we where leaving in the morning.
Men are expected to have short swim trunks or speedos.
My son and I had board shorts which are swim trunks that look like regular shorts. They where also a problem because the covered too much leg and had a zipper.
My wife and son ended up getting a refund and did other things. Looking back I should have done the same. While the water is nice, the whole question of wearing too much swimsuit at the spa designated for swimsuits was really annoying.
I hope this helps other travelers.