Two sets of Stone Age footprints, estimated to have been formed sometime between 5,000 B.C. and 2,000 B.C., were found in the island of Lolland in Denmark. The prints were discovered in a dried up fjord in the area where the Fehmarn Belt Fixed Link will be built. The Fehmarn Belt Fixed Link is an underwater tunnel that will connect the Danish island to the German island of Fehmarn.

"This is really quite extraordinary, finding footprints from humans," Terje Stafseth, an archaeologist at the Museum Lolland-Falster, said in a statement. "Normally, what we find is their rubbish in the form of tools and pottery, but here, we suddenly have a completely different type of traces from the past, footprints left by a human being. We are familiar with animal footprints, but to the best of my knowledge, we have never come across human footprints in Danish Stone Age archaeology before."

One set of prints is smaller than the other, signifying that they belong two different individuals. 

Lars Ewald Jensen, the Museum Lolland-Falster's project manager for the Fehmarn Link project, spoke to Live Science and explained that the owners of the footprints, along with other prehistoric Lolland people, used the area as fishing grounds, and they built elaborate fish traps or fishing fences.  Since the prints were found on each side of a fence pole, one theory is, the individuals were recovering their traps prior to an incoming storm. Their feet sunk deeper into the soil as they tried to pull off and move the post, and when the storm came, fine layers of mud and sand covered the footprints, thus preserving them.

Other than fishing, the area may have also been used to offer sacrifices to the sea.

"They put fragments of skulls from different kinds of animals [on the sea floor], and then around that they put craniums from cows and sheep," Live Science quotes Jensen as saying. "At the outermost of this area, they put shafts from axes. All in all, it covers about 70 square meters [83 square yards]. It's rather peculiar."

In an estimated year or so, the archeologically-rich site will give way to the construction of the Fehmarn Belt Fixed Link, and while the tunnel will be below ground, facilities will be built above-ground. The project will cover the discovery site, and archaeologists are doing their best to find more artifacts before they disappear forever.