The day before these photos were taken we already had a long walk and tried to come to the viaduct without success. Reason for the confusion is that there are actually two viaducts. The "Smardale Viaduct" which is part of the still active Settle Carlisle Railway line and the "Smardale Gill Viaduct" which is no longer in use and now part of a scenic walk through the gill. On our ill fated walk a farmer explained to us how to get to Smardale Hall car park near the viaduct (on map 1 at the top right corner and on map 2 at the bottom. For some strange reasons the two information boards are mirror imaged). We went there without problems the next day and we were able to follow the former railway track until we came to the viaduct, crossed the viaduct, had a good look at the huge lime kilns, returned to the beginning of the viaduct and went on a small path on the other side of the ravine to get a good view of the viaduct. 

P.S. Please note how my wife is patiently waiting for me on photo #11 while I stumbled across the hillside looking for good photo vantage points!