The waters off the glittering coastlines of Britain's Caribbean territories have long been a mystery.
But now scientists on the first expedition beyond the islands' shallows have discovered an underwater mountain range, a massive "blue hole", coral reefs apparently untouched by climate change and never-before-seen sea creatures.
Operating 24 hours a day for the last six weeks, researchers subjected cameras and other equipment to extreme water pressure, recording as deep as 6,000m (19,700ft).
To navigate the Cayman Islands, Anguilla and Turks and Caicos, they were forced to rely on decades-old maps with serious errors and whole areas missing.
The UK Centre for Environment, Fisheries and Aquaculture Science (CEFAS) has shared their footage and discoveries exclusively with BBC News.
