Follow the disused Hatfield to St Albans railway line on this route from St Albans to Hatfield. It is a shared cycle and walk path and makes for an easy and safe stroll or ride. The route runs for about 6 miles with nice views of the countryside along the way.
If you enjoy this ride then you could also try the Cole Green Way. It's another traffic free rail trail running from Welwyn Garden City to Hertford.
See the St Albans Cycle Routes page for more rides around the area.