This video from 1953 shows an advertisement for an outdoors salt water wave pool called Bad Boekelo.
The film is called Zee op de Heide, ‘Sea on the moor’, which is ironic because Boekelo near Enschede is about as far away to the east of the North Sea as possible in the Netherlands. The video describes the wave pool from about 2 minutes in: “An ingenious construction with two mechanically moving doors creates a real surf.” The hotel was built to give the business people dealing with the nearby salt industry a place to stay, and filling the pool with the salt from nearby salterns must have been a nice gimmick.
The hotel still exists, but the wave pool (which was built around 1934) has been turned into a pond. The name of the salt company, then called Koninklijke Nederlandse Zoutindustrie, still survives in the KZ of Akzo Nobel.
Note that completely by accident this has become the third posting in a row where I describe the demise of a notable pool or resort in the Netherlands.
(Video: Youtube / Historisch Centrum Overijssel. Image: still from the video.)