Crypt of Balbus. After 20 years of excavation and restoration, these fascinating remains of a porticoed courtyard and theater built in 13 BC, now part of the Museo Nazionale Romano, afford a unique look at Roman history. Rather than focus on one era, the museum peels back the layers of the site, following the latest techniques in conservation. The well-explained exhibits (with text in English and Italian) give you a tangible sense of the sweeping changes that this spot -- and Rome -- underwent from antiquity to the 20th century. A partially restored wall provides an example of what marble and tufa constructions looked like before weather took its toll and medieval builders stripped the marble off for reuse. Copies of documents and reconstructed coins and other everyday objects found in drains, rubbish dumps, and tombs are a window into the world of the people who lived and worked here over the ages. COST: EUR4.