The 4-foot gauge Saundersfoot Railway was Pembrokeshire’s first and carried coal from nearby pits to the local harbour. It comprised two main lines, one of which headed up a 1:5 incline and through a tunnel of around 490 yards to Broom, Thomas Chapel and Reynalton collieries. The 1st March 1834 marked its opening.

The line was relaid in the1870s to facilitate the use of locomotives (previously the wagons were horse-drawn) but, by the outbreak of World War II, the pits had closed and the line fell into disuse.

The tunnel is mostly lined in masonry although later repairs have been carried out in both red and engineering blue brick. A substantial retaining wall ajoins the south portal and, at that end, the tunnel passes beneath the operational line to Tenby. Towards the middle, an adit disappears off at a right angle.

Water flow through the bore is considerable at times whilst the mud on its floor can prove quite deep.