Baths of Caracalla

An imperial bath complex completed in 216 AD that could serve 1,600 bathers at a time across hot, warm, and cold rooms, swimming pools, gardens, libraries, and gymnasia — an entire civic centre under one roof. The vast surviving brick walls give a real sense of the scale of Roman public architecture, and the original mosaic floors are still in place across much of the site. Free entry on the first Sunday of every month, and the ruins host outdoor opera performances each summer — Rome's most atmospheric concert venue.