I know that there was at least one rooftop pool in London by osmosis, and that there had to be others for the reason that there had to be hundreds of hotels in London and at least a few of them were created by builders with more money than sense.

Cardiff has less hotels, so I figured the builders had less chances to strike the lottery of rooftop pools.

( I just looked at the Berkley hotel. I'm sorely tempted just to dump bodies in their pool just to spite them. I have no idea what to do afterwords, though, hence the plea... )