In the West End of the Roatan Island of Honduras you can go diving in a "home built" submarine, Idabel, to 2,400 feet (a record depth at that time that has been beaten since) with Karl Stanley, the submarine builder/owner. Karl has been featured in many articles and a National Geographic documentary and I had an amazing opportunity to explore the deep sea twice with him.
Seeing underwater creatures where not many humans have been is simply humbling.
Dumbo Octopus and a six gilled shark are just a couple of the unique animals found only by going deep. Sadly, also Coke cans make it to the bottom of the vast ocean.