In Wien, you can just walk into train stations and subways without having to pass through a turnstile. However, when about to leave Wien for Praha, I did see one very secure Plexiglass gate, with a €0.50 fee to pass through. It was the only area where they didn't trust people to pay, so I decided to check it out.
The charge was to enter the only unclean toilet in Austria. There were soap suds in the sinks, and the paper towel dispenser was broken.
I guess this was a museum exhibit intended to show travelers what to expect if they left Europe.