The answer to Photo Quiz No.37 is it’s the Cumberland Obelisk at Windsor Great Park, located not far from the car park at Savill Garden. Commenter lightwater retiree knows where it is, though not what it’s for, though rightly knowing about Culloden.
Wikipedia says THIS about the obelisk,
Beside a smaller lake, known as the Obelisk Pond is the Obelisk memorial to the Duke of Cumberland. This is inscribed
THIS OBELISK RAISED BY COMMAND OF KING GEORGE THE SECOND
COMMEMORATES THE SERVICES OF HIS SON WILLIAM DUKE OF CUMBERLAND
THE SUCCESS OF HIS ARMS AND THE GRATITUDE OF HIS FATHER
THIS TABLET WAS INSCRIBED BY HIS MAJESTY KING WILLIAM THE FOURTH.
It was originally inscribed “Culloden” but this was erased on Queen Victoria’s orders and replaced with “CUMBERLAND”: “CUMBERLAND” is inscribed within an inset in the masonry, the original surface having had “Culloden”.