Haus des Meeres (House of the Sea)

This guide to Haus des Meeres in Vienna starts with concrete over three metres thick, raised by forced laborers in under a year as one of six flak towers architect Friedrich Tamms designed to defend the city. It follows the windowless fortress through its strange postwar afterlife as a hotel, a fire station and a youth hostel, before a handful of volunteers let themselves in one November evening in 1957 with an idea for what to do with it next.