In 373 BCE the classical Greek city of Helike disappeared beneath the waves. Its destruction was so catastrophic that the only way the Greek authors could make sense of it was to blame it on the supernatural - Poseidon destroyed the city. It's hauntingly similar to the myth of another Ancient civilization lost beneath the waves - Atlantis. Helike's location is one of the greatest mysteries in archaeology, but could it be possible to rediscover the lost city and could Helike actually be Atlantis?