• Plan 20 to 30 minutes for the walkway loop above the ruins at kid pace, then let legs loose in Ciutadella Park, five minutes away
• Make it a spotting game: wells, drains, and street corners are all visible from above, and the site reads like a life-size map of a buried town
• Open until 8pm most of the year, with last entry to the excavation 30 minutes before closing, so it works as a late-afternoon stop

The city's grand iron market hall, built in 1876, was being turned into a library when workers found an entire block of 1700s Barcelona under the floor: streets, houses, shops, and drains, left where they stood after the siege of 1714. Today you walk in free and look over the whole excavation from the balustrade that rings the hall, which lands even with kids because it looks exactly like what it is, a buried little city. Ticketed exhibitions and guided visits take you down among the ruins themselves. Closed Mondays. It also makes the perfect basecamp for a wander around El Born itself: Santa Maria del Mar, the basilica everyone calls the cathedral of the sea, is three minutes one way, Ciutadella Park five minutes the other, and the narrow passageways between them hide tapas bars for the grown-ups and calm playground squares for the kids, like Plaça del Pou de la Figuera.