I’m looking for somewhere similar to Kestrel in London - naked day spa where you can show off, where there will be girls - so not a gay sauna. Is there anywhere like this? Any help is appreciated!

The Netherlands has hundreds of saunas where being naked is both entirely normal and mandatory when visiting. They're not really places to "show off" though; they're just a place that Dutch people like to go to have a day to relax. Dutch people often go to them with their friends and/or family.

I've only been to one once, but it's definitely an experience I'd recommend trying.