Cartagena de Indias is a major city on the Caribbean coast of Colombia. The old city is surrounded by defensive walls and is a well preserved example of colonial Spanish architecture. The new city is a mass of tower blocks and there's heavy industry further out in the bay.
I booked to go diving with Diving at their office in the old town. The price was $316,000 (about US$105) as I paid cash. They did take credit cards but it was an extra 5% on top. This price included insurance, so they need a copy of your passport. I had my own but it was only $3,000 of the price anyway.