In 1917, due to coastal erosion, the railway line between Bray and Greystones was deviated inland for the final time (for the moment!) with the construction of Bray Head No. 4 Tunnel. This commenced almost immediately south of Bray Head No. 3 Tunnel and replaced a long section from there to just north of the harbour at Greystones. Part of this route had already been deviated in 1888 – the remains of which can be seen on GoogleMaps:
At 1,084 yards long, this is the second longest railway tunnel in use in Ireland and just north of the south portal, there is an air vent.
Very few photos of this exist and I am not surprised. It is located on private land and is not accessible from nearby roads nor the Bray Head cliff path.
I went out to Greystones today to see how close I could get and the photos below are the best I could achieve: