Blick Mead

Blick Mead is a chalkland spring in Wiltshire, England, which has a constant temperature of around and never freezes. It is close to an Iron Age hill fort known as Vespasian's Camp and about a mile from the Stonehenge ancient monument. Archaeology at the site conducted since 2005 shows human habitation going back to 10,000 BP (8,000 BCE) and to be continuous until 6,000 BP (4,000 BCE). 
35,000 worked flints and 2400 animal bones, some cooked, mostly from Aurochsen, have been found at the site. There is also the remains of a pit dwelling. These have been used to radiocarbon date the time of settlement. It is thought that the site would have been an attractive place to camp or dwell with a spring that never freezes over.
A rare algae called "Hildenbrandia" lives in the spring and it causes stones taken from it to turn bright red on exposure to air in a matter of hours. In Mesolithic times this could have given the place a magical significance. Its closeness to Stonehenge has led to theories that it is the original attraction that brought hunters to the area, with the colour-changing stones giving the place a spiritual significance in their culture.