Panamá Viejo is what remains of the original city of Panama, founded by Spanish conquistador Pedro Arias Dávila in 1519 — one of the oldest continuously occupied European settlements on the Pacific coast of the Americas. The city was sacked and largely destroyed in 1671 by the Welsh privateer Henry Morgan, who led an overland raid across the isthmus with around 1,200 men, looted the city, and left it in flames. Rather than rebuild on the same site, the Spanish founded the new city — today's Casco Viejo — a few kilometres to the west on a more defensible peninsula.
What survived Morgan's raid is now a park at the eastern edge of the modern city: a spread of ruined stone walls, arches, and towers rising from a flat expanse of grass with the glass towers of the contemporary skyline visible beyond. The most recognisable structure is the cathedral tower, which still stands to nearly its full height and is the symbol of the ruins. A small museum on site gives context about the founding of the city, the colonial trade in gold and silver that made it wealthy, and the raid itself.
The ruins are a UNESCO World Heritage Site (shared with the Casco Viejo). They are less immediately spectacular than a site like Cartagena or Antigua, but the setting — a medieval Spanish ruin with a twenty-first century Latin American skyline behind it — is unique, and the museum is worth an hour.