In previous centuries, rails were used as a way to democratize transport of most people to long distances. This is specially true in the rural Spain. As a result, long infrastructures crossing forests and mountains were built. This intelligent idea lasted for decades, but ultimately the bad economic situation provoked a massive migration from villages to cities. Some stretches of railroad stopped being use and lack of support made the rest. Alternatively, the rise of alternative ways of transport, mainly the car, reduced the use of rails.
Under so dismal situation and thanks to open-minded people, these infrastructures which are the backbone of large rural areas have became a good boost to promote cycle tourism. Some EuroVelo are indeed rail trails. Of course, they set up them since some were deteriorated as time went by. There is an additional point which makes it possible: only bicycles and pedestrians are allowed to enjoy them, giving them extra safety. Moreover, the spectacular landscapes, the suitability of curves plotting, the environment, forests, mountains or even cheering, happy people you meet in rail trails constitute all points in favor.
At the time I am writing this post, you can find the sections Where to go, What to do, Plan your trip, Calendar of events and Travel safe with a lot of information in the Green Paths webpage.
There are also rail trails at least in Bermuda, Canada, US, Germany, UK, Ireland, Belgium, Finland, Australia, New Zealand and Singapore. Thousands of kilometers are waiting for you and your bike.