The city's colonial fortress has been almost swallowed up by the modern port, and you have to squint to pick it out amid the container ships and cranes across the harbor. The central part of the fortress was a prison, and a notoriously inhumane one, during the Porfirio Díaz regime. Today, San Juan de Ulúa is an empty ruin of passageways, battlements, bridges and stairways undergoing lengthy renovations. Guided tours are available in Spanish and, quite often, in English.

The fort was originally built on an island that’s since been connected to the mainland by a causeway. The earliest fortifications date from 1565 and a young Francis Drake got his comeuppance here in a violent battle in 1569. During the colonial period, the fort and island became the main entry point for Spanish newcomers to Mexico.

To get here, you can take a taxi (M$50) or, weather permitting, a lancha (boat taxi; M$30) from the malecón (beach promenade).

Entry is free on Sundays.