Disused m Snoqualmie Tunnel closed 50 years ago as part of sweeping closures . Engineers due to visit 3,148m tunnel next week for first time since it closed . Cyclists could retrace steam locomotives ' route from Rhondda to Swansea . It would be world 's second longest cycle tunnel , after 4,000Rhondda Tunnel near Seattle , U.S .
Disused Rhondda Tunnel closed 50 years ago as part of sweeping closures . Engineers due to visit 3,148m tunnel next week for first time since it closed . Cyclists could retrace steam locomotives ' route from Rhondda to Swansea . It would be world 's second longest cycle tunnel , after 4,000m Snoqualmie Tunnel near Seattle , U.S .