1km of woodland by railways sounds good to me. What's the drawback?
Some of the closed ones have already been upgraded into Cycleways or downgraded into carriageways. Does anyone know how many closed lines are unobstructed? I don't think any in Norfolk haven't been built over or turned into roads at some point: the closed Lynn lines are blocked at Wolferton and Hunstanton on the way to Hunstanton (8 miles to the blockage, royal estate housing), Hillington on the way to Fakenham (maybe 7 miles, road on the trackbed), Narborough on the way to Swaffham (12 miles? Nature reserve on the trackbed, endangered species) and West Lynn towards Spalding (2 miles? Road on the trackbed for at least 10 miles). I think even the Watlington to Wisbech line which makes little commercial sense IMO because its Watlington junction faced away from London/Cambridge and it has expensive river and drain crossings missing has lost its route into Wisbech.
Some would make great Cycleways but only the first few miles of two do so far, but I'll be surprised if any return as railways. The most likely is probably the Hunstanton line if Charles ascends and wants his train to get closer than its current terminal at a quarry, as he'll remove the blockage and local government will see it as a way to reduce the holiday traffic problem as well as demonstrate their monarchism with our taxes!