Cathedrals and churches are all around the Old City and they’re all interesting to visit. The Metropolitan Cathedral Basilica of Saint Catherine of Alexandria (known simply as La Catedral de Cartagena and you can see its steeple from outside the wall) is located across Bolívar Square.
Iglesia de San Pedro Claver is perhaps more famous for its patron saint. It’s a three-story wonder and has pre-Colombian art exhibits and was built in the late 1500 to early 1600s. Saint San Pedro Claver (1580 – 1654) was Spanish Jesuit priest who dedicated his life to helping African slaves in the 17th century and was canonized as the “slave of slaves.” You can enter the church, check out the massive organ, narrow but reverent nave, high ceiling with stain glass windows, and see the simple living quarters of San Pedro Claver.
If you’re in Plaza de Santo Domingo, visit the oldest church, Iglesia de Santo Domingo, which was built and rebuilt in the early to mid 1500s. There is also a Santo Domingo church on Calle Sargento Mayor (corner of Calle 38 and Carrera 6).