Chris Packham visits a peculiarity of the Breckland landscape - the pingo. Also known as a kettle lake, it is a very rare type of pond. There are dozens here - in the largest density in the UK. They were created at the end of the last ice age and have been left almost untouched since then. Chris demonstrates how they were formed with a lump of ice and a mole hill. As the glaciers retreated they left hard lenses of ice pressed into the ground, with soil over the top of them. When things warmed up and that ice melted the soil would have formed a depression, and their meltwater forms a pond in the hollow. Elsewhere in the UK most pingos have been ploughed up. Pingo is the Eskimo word for hill.