Not exactly "on the line" but I have been researching Avebury and Lacock ... as a trip from London without a car.   Although they are both major National Trust sites, and just 10 miles apart, it's not easy and impossible on a Sunday.

I was interested in this page that gave me alternative ways (to the car) to get to Avebury:
http://www.wiltshire.gov.uk/leisureandculture/museumhistoryheritage/worldheritagesite/howtotraveltoavebury.htm
listing on order foot, cycle, horseback and bus.

Now wouldn't a "Travel Wiltshire Tourist Guide" be really useful - to help visitors sort out these things for themselves, encourage more to wiltshire, help the local economy ...