Between two sources of the River Thames
The official source of the Thames is near Kemble, but the water from Seven Springs also goes into the Thames. Seven Springs is higher than Kemble, flows all year and would make the Thames longer. There are also two plaques in latin saying that it is the source. This is a walk through some Cotswold villages (more if you want detours) between the two sources.
Hike
Andrew Phillips-Godfrey on scottexservices.com