I walked through Hose tunnel on the former LNW & GN Joint line from Bottesford to Melton Mowbray in 1982 and nearly had a serious accident. There was a manhole cover missing in the middle of the trackbed and I "just" managed to stop myself falling!
http://www.flickr.com/photos/pinzac55/3555273514/
http://www.flickr.com/photos/pinzac55/3555273514/