A team of explorers working off the western coast of Cuba say they have discovered what they think are the ruins of a submerged city built thousands of years ago. Researchers from a Canadian company used sophisticated sonar equipment to find and film stone structures more than 650 metres below the seaâs surface. The explorers first spotted the underwater city last year. In July this year the researchers returned to th site with an explorative robot device capable of highly advanced underwater filming work. They believe the formations could have been built more than 6,000 years ago, a date which precedes the great pyramids of Egypt by 1,500 years.