Free walking routes
Here is a link to the "Walking in Wilts" website. You might find some helpful information on suggested walking routes. http://www.walkinginengland.co.uk/wiltshire
Wessex Wanderers Train Walks
The Wessex Wanderer is a programme of Public Guided Walks from stations on the Bristol to Weymouth Railway Line, which is organised and led by volunteers of the Avon, Dorset, Somerset & Wiltshire Areas of the Ramblers' with support from the Heart of Wessex Rail Partnership and First Great Western.
More information about these walks, including the programme, can be found on the Wessex Wanderer website.