Vienna has a scattering of public toilets that are suitably clean and cost about €0.50 to use. Metro stations invariably have decent public facilities. Public toilets are less common outside the big cities, but you can usually use the facilities of hotels and restaurants without too much fuss. It's courteous to purchase something in a bar or restaurant beforehand, but this is rarely a problem and nothing that can't usually be resolved with a smile and a Danke. Gas stations along highways usually have restrooms attached, and these are generally open to the public whether you purchase gas or not. Cleanliness standards vary, but are usually on the acceptable side.
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The Bathroom Diaries. Flush with unsanitized info on restrooms the world over—each one located, reviewed, and rated. www.thebathroomdiaries.com.