Three Counties Trek - Charity Walk Rise to the Challenge and trek a marathon to help save lives with Thames Valley Air Ambulance. Join our charity walk and trek through our three counties (Berkshire, Oxfordshire and Buckinghamshire) along the River Thames. We have two routes available, see below for the itinerary and routes. Oxfordshire - Buckinghamshire - Berkshire: 26 miles The charity walk starts at around 6am from Hambleden Estate, Oxfordshire. The route follows the River Thames from Oxfordshire, into Buckinghamshire and finishing at Windsor Racecourse in Berkshire. At 26 miles long this is a real challenge for anyone, one that will be physically and mentally demanding. Rise to the Challenge - Register today Burchetts Green - Windsor: 13 miles Starting just after lunch, this route is the second half of the 26 mile walk. Burchetts Green is the beginning of the 13 mile route, after which we leave the urban area of Maidenhead to join the Thames Path towards Windsor Racecourse to finish in the evening. Rise to the Challenge - Register today Registration Entry is just £25. Your entry fee covers the cost of your participation on the charity walk. We ask each walker to kindly aim to raise £250 (13 mile) and £300 (26 mile) minimum sponsorship to help save lives across our region.