The road starts on the B8, on the eastern outskirts of Hilltown, and heads southeastwards. The route is a very scenic one, passing through the Mourne mountains over the Spelga Pass (1200 ft) and along the Spelga reservoir. It is one of the few roads on the island of Ireland to have relatively frequent closures due to snow, and an avalanche risk led to its closure in March 2013.
The original terminus of the B27
The current southern terminus of the road is on the A2 in the centre of Kilkeel. However, in the original 1923 road numbering, the B27 extended beyond Kilkeel to Greencastle Pier to connect with the ferry across the mouth of Carlingford Lough to Greenore, County Louth, which seems to have been an important ferry route at that time. This 1923 terminus would have made it the southernmost classified road in Northern Ireland. This section of road seems to have been declassified by the 1940s; it is now the C365. A ferry service resumed in summer 2017, a project opposed to by many in the Greencastle area, partly owing to the traffic implications. The Greenore-Greencastle crossing is just 1.1 miles by sea and takes just 15 minutes, cutting out a 33-mile car journey passing through Warrenpoint, Newry and Omeath.