Part of the MuseumsQuartier, the Architekturzentrum Wien collectively encompasses three halls used for temporary exhibitions, a library and a cafe. Exhibitions focus on international architectural developments, and change on a regular basis (admission can by anything from free to upwards of €24). The extensive library is open to the public. The centre also organises regular walking tours through Vienna on Sunday (in German), covering various architectural themes. You need to book ahead; see the website for dates and prices.