This was an entrance to the fortress of the island Tierra Bomba about 10-15 mins from Cartagena #Colombia. Really interesting fortress with clever architectural features. And some pitch-black corridors full of little bats! And yes we did walk through them! A visit to Tierra Bomba with the public ferries is a more tranquil option compared to Isla Rosario and other more commonly visited islands. Go off-the-beaten-track and come here!