There are two tunnels south of Guildford station, where the line to Godalming, opened in 1849, passes under the eastern tip of the Hog's Back. Unusually, neither is the same length as when it was first built.

Guildford Chalk Tunnel, photographed on 20th September 2009. photograph by Gregory Beecroft

The London & South Western Railway had few lengthy tunnels, and Chalk Tunnel, at 845 yards, is the longest on the electrified lines from Waterloo. It was originally longer, at 968 yards, but the northern end was excavated out. The portals are quite plain, but there are the remains of an overbridge immediately in front of the north portal. The up line is bi-directional between Guildford station and Shalford Junction, hence speed restriction signs for both tracks.

This is the southern portal of Chalk Tunnel. photograph by Gregory Beecroft

Guildford St Catherine's Tunnel, photographed on 20th September 2009. photograph by Gregory Beecroft

Part of St Catherine's Tunnel collapsed in 1895, apparently because of percolation of water from a burst water main. About 1,000 tons of debris fell onto the line, narrowly missing a train. A coach house and stables over the tunnel fell into a hole 48 feet wide and about 18 feet deep.

The tunnel was extended at its north end in 1984, in order to provide additional support for unstable ground above. The new section comprises concrete sections on brick abutments. Despite this work, the length of the tunnel is still quoted officially as 132 yards, the same as that shown in Southern Railway records. The photograph shows the new construction, and also the position of the old portal, a short distance inside the tunnel where the wall steps in.