For some reason I looked into this a couple of weeks ago, and discovered there's one in Amsterdam pretty close to where I often work, in the Grand Hotel Amrâth. It's supposedly open to the public every Sunday between 10am and 2pm. I think it's only the second time I've seen one in person, and the previous one has been demolished.
Only place I've ever come across one was Napier College, Edinburgh in the mid 1970s. I found it quite scary, and actually preferred to take the stairs. I seem to remember it was actually shut down, for undisclosed reasons.
I also used these ones in Edinburgh decades ago, and the same model at Leeds uni which was a similar vintage. The Napier one there is a story about a lecturer convincing two students it went upside down and if you tried to loop the loop you had to stand on your hands to do the transition... much hilarity when they appear upside down on the other side.
