Head to the Gothic Quarter—once home to Barcelona's storied Jewish neighborhood, El Call—and look for the Sinagoga Major (Major Synagogue). The museum, built on the site of the city's oldest temple, is only two rooms, but it contains a stadium's worth of history. For just 2 euros, you'll get a tour of the excavation site and a riveting tale of the Jewish faith in Spain—plus an entertaining ancedote about how the ruins were discovered. Nearby, you can sign up for a guided tour of El Call, or shop for books and kosher products at the Barcelona Call Store. The synagogue is open Monday through Friday from 10:30 a.m. to 5:30 p.m. and Saturday and Sunday from 10:30 a.m. to 2:30 p.m.