A feat of Spanish colonial military architecture, the Castillo San Felipe de Barajas is one of Cartagena's most prized attractions. The fortress, whose construction finished in the late 18th century, was never seized — and not for a lack of attempted forays. Part of its sophisticated system of underground tunnels is open to the public. A guided tour (audio guides available) is highly recommended.

This beautiful example of Spanish colonial architecture contains a small museum dedicated to the Spanish Inquisition's brutal persecution of heretics once carried out in these very chambers. Visitors can still see some of the torture devices used to extract confessions of heresy and witchcraft, along with some of the questions used in "witch" interrogations, which are still displayed on the museum wall. Needless to say, no prisoner could hope to be acquitted of their purported crimes against the Catholic Church, and most met their tragic end at the very guillotine still on display in the courtyard.

It is possible to have a combined tour of Paul McCartney's childhood home and Lennon's. The house is now a part of the National Trust, which is also the only authorized ticket seller. It is necessary to arrive at the sight with your tickets already bought at the website below.