Here’s the 2002 English Heritage description of Kelston Park, the estate of which Kelston Roundhill was formerly a part. It offers a thorough and concise description of the history and layout the estate. It’s pretty dry (won’t even stoop to using Lancelot Brown’s more familiar nickname), not big on illustration, but informative (click for more).
It refers to Kelston Round Hill “a landmark hilltop crowned with a group of beech trees and visible for many miles around” and says:
a track 850m north of Kelston Park leads 500m south-east through Sandpit Shrubbery and Shagbear Wood and runs for c 1km in an easterly direction before turning north-west on the Cotswold Way for 1km over Dean Hill to the ornamentally planted 218m summit of Kelston Round Hill. This route was an C18 ride from the park to take in the unbounded views available from the high ground to the north.
It describe Kelston Park’s vast octagonal brick structure as a stone kitchen garden. But the more intriguing explanation offered by local writer and broadcaster Martin Palmer is that is that for a century and a half it was used for raising Arab stallions (which accounts for unusual local use of brick which gets warmer than local stone). We’ll put it to Martin, who has offered to do a video interview about the Roundhill.