Map showing extent of Doggerland, a vast territory in northwest Europe that was above sea level 16,000 years ago, and the territory's diminishing size as ice melted and the North Sea rose. Illustration by Claus Lunau/Science Photo Library.
Via https://sciencemastodon.com/@ebender00/113606996477811407
Doggerland was discovered when a dredging trawler brought up a block of peat and they found a stone tool inside. They were, of course, initially mystified about how a stone tool could end up inside peat under the ocean.