Old Warden Tunnel
Old Warden Tunnel is an old disused railway tunnel dating back to 1857. The tunnel was built as part of the Midland Railway connecting Bedford and Hitchin. The tunnel is perfectly straight, total length is 882 yards and it runs at a slight gradient to allow drainage.
There are rumors that the tunnel is haunted but I saw no signs of paranormal activity whist down there. Although there were a few bats which did make me jump when they started flying around above my head.
Entrance to the tunnel is via a small hole as seen in the photo below.