The Lost Land takes us on an underwater trip to a world that's gone – but still there, hidden in the dark waters of the Baltic Sea, 30 meters down. Buried under sand and swallowed by the dark are the remains of forests that grew here 12,000 years ago – pines and oaks. So far, around 100 old tree remains have turned up, some still with roots, branches, even tiny twigs, sitting 25 to 32 meters deep. The scientists want to find whole stretches of these old forests, take samples, and test them in the lab to work out how old the trees are and where they came from. It's a big find – one that's changing what we thought we knew about the Baltic coast's history and the people who once lived there.