Door with Fish Door Knocker (or Aldaba) in Old Town, Cartagena de Indias, Colombia. Cartagena has the world's largest collection original knockers. The knockers are usually bronze, and in medieval times they indicated social status and wealth. Sea creatures indicated the homes of merchant seamen; Lizards for royalty; Lions for military; Owls for educators; Dogs for slavers; and Hands with Jewellery for clergy and aristocrats who fed the poor.
This is an old Spanish Fort in beautiful Cartagena, Colombia that they used back in the days when Colombia was fighting for its independence from Spain. The tunnels underneath go several miles below sea level. I was there in 1978.