What is this I am sat on today!

We stopped off for a coffee this afternoon at Pendle Heritage Centre and came across this circle. there are two of them and I haven't a clue what they are.

Pendle Heritage Centre was once home to the Banister family a couple of hundred years ago.

Sir Roger Banister was the first man to achieve the four minute mile and his father was born in Trawden. I will blip that cottages another day.