Bath tunnel ultra marathon a 'mind-bending' test
"You've got to be a sandwich short of a picnic to give it a go."
That is the verdict of Tunnel Ultra runner Karl Baxter, who entered a 200-mile marathon in a disused railway tunnel in Bath.
Participants have to run the distance in 55 hours in pitch-black darkness. Many do not finish and one entrant went temporarily blind in previous years.
The challenge is described as a "mind-bending test of extreme endurance and sensory deprivation".
Video journalist: Alex Howick