National Library of Technology

Best place to work if you're staying longer in Prague. Entrance is free, but if you're not a student (eduroam) or not registered, you won't have free wifi. Registration is cheap (50 CZK for half a year) and could partly be done online, but you need a card with a chip, otherwise you pay 200 CZK for the card. Some parts are very quite and have comfortable chairs and tables to work, other parts are louder and allows you to make calls.