The good thing about old rail lines is that the railbed is usually still intact and level. They make great walking or bike paths because they are generally wide enough and the gradient is low.
There is one in particular in our province that I wish could be turned back into an inter-urban rail line, but they have been talking about it for 20 years without anything being done, except more transit studies. With highways being so crowded, and cities sprawling into suburbia, you would think governments would invest in short rail lines for public transit.
That tunnel looks interesting. We rode bikes along a disused rail line, including wooden trestle bridges and tunnels, and it was an exceptional experience.