Malham Tarn, North Yorkshire, England

You don't find a lot of lakes or reservoirs in the Yorkshire Dales because limestone is too porous a rock when it comes to the business of holding water. That also makes it good caving country, if you are into that sort of thing. So, Malham Tarn's existence is rather remarkable, but it is a consequence both of the Craven Fault's throwing up of a bed of Silurian slate and damming by a terminal moraine after the last ice age. The Pennine Way makes its way around the tarn on its journey towards Fountains Fell.