Over 40 walks (linear and circular) along the line from Nottingham to Matlock.  This site is run by the Derwent Valley Line Community Rail Partnership. 

This site is run by the main train operator for the region - and the East Coast mainline.  Their site includes a blog with six scenic walks (mainly descriptive).

Walks from stations along the Hope Valley Line, which crosses the Peak District from Sheffield to Manchester.  This site is run by Marketing Sheffield, part of Sheffield City Council.  

Walks along the line from Grantham to Skegness (linear and circular).  This site is run by the Poacher Line Community Rail Partnership. 

Dozens of circular and linear walks by public transport (rail and bus) in the midlands counties.

Eight circular walks starting from Buxton station, in the Peak District, downloadable as a pdf.  Created by Friends of Buxton Station for the Buxton Town Team.