The Kilmacthomas Viaduct dates from 1878, when it was part of the newly built Waterford & Dungarvan railway which went all the way to Lismore, and overcame many difficult engineering challenges through occasionally spectacular scenery.
Partially closed in the mid 20th century, and after decades of intermittent operation ending in the 1990s, it was turned into a greenway (a special cycle path) in 2017; indeed, one of the most successful in Ireland, since it apparently attracts upwards of a quarter of a million visitors a year.
This shot is from a drone looking towards the Comeragh Mountains, and you can trace the curve of the greenway (and old railway line) into the distance from the foreground. An impressive feat of engineering, and a wonderful cycle. I heartily recommend visiting.