Hidden House in Porto

On the Rua do Carmo, in central Porto, Portugal, two churches stand side by side, so close that they appear to be one building. They are the 17th-century Igreja das Carmelitas nunnery and 19th-century Igrejo de Carmo monastery. In fact, the two churches are separated by one of the world’s narrowest houses, no more than one meter wide and yet three stories tall, known locally as the Hidden House.

Actually occupied until the 1980s, the Hidden House is now a museum that can be toured. The museum and churches are open 10 a.m.-6 p.m. Tues.-Sun. and 12-6 Mon. Entry to the museum is through Igrejo de Carmo, and the door charge of €3.50 (near $4) covers both and the catacombs. The Igrejas das Carmelitas is free to enter.