Catedral de Santa Catalina de Alejandría

This guide to the Catedral de Santa Catalina de Alejandria in Cartagena follows master builder Simon Gonzalez, chosen in 1575 to raise the new cathedral not from granite or quarried limestone but from coral rock cut from the seabed off Tierrabomba island. Partway through construction, with the walls already rising around him, he tested that porous, fossil-flecked stone under load and didn't like what he found, redesigning his original plan of six paired columns on the spot. Look closely at the walls and you can still make out the shapes of ancient coral heads and sea creatures in the stone.