A team of explorers led by Poland's Krzysztof Starnawski has discovered what they claim is the world's deepest underwater cave at 404 metres. The cave, 'Hranice Abyss', which was found in Czech Republic, surpassed the previous record by about 12 metres. Starnawski first dived to reach 200 metres and then used an underwater robot to reach another 204 metres.