Museu d'Història de Barcelona (MUHBA) — Underground Roman Barcino

Beneath Plaça del Rei and the medieval Palau Reial Major lies one of Europe's most extensive underground archaeological sites, accessible via the Museu d'Història de Barcelona (MUHBA). A walkway of roughly 4,000 square meters winds through the excavated remains of Roman Barcino, founded in the 1st century BCE, letting visitors walk at street level among Roman-era workshops, laundries, wine and garum (fish sauce) production vats, and residential foundations. The route traces the transition from a working Roman colony into the seat of an early Christian bishopric, culminating in the remains of a 6th-century Visigothic episcopal complex with its baptistery and assembly hall, layered directly above the Roman streets. Interpretive lighting and walkways were designed to preserve the archaeological strata while making the site legible to non-specialists, and multilingual panels explain each functional zone, from dyeing and food-production areas to domestic quarters. The excavation, carried out in stages through the 20th century as the medieval square above was restored, remains one of the most significant urban digs in Spain, because it captures an entire cross-section of a Roman colonial town rather than isolated monuments. The site connects directly to the Palau Reial Major and Saló del Tinell above ground, allowing visitors to move chronologically from Roman Barcino through the Visigothic period into the medieval Counts of Barcelona era within a single MUHBA ticket. Restoration and conservation are ongoing, with climate-controlled sections protecting fragile plaster and masonry. The underground circuit gives one of the clearest pictures available anywhere of how a provincial Roman city functioned day to day, from industrial production to civic administration, and how that city's institutions carried forward into the early medieval world.