A mind-bending test of extreme endurance and sensory deprivation: 200 miles through the UK's longest foot tunnel, Combe Down Tunnel in Bath. Runners complete 100 out-and-back laps of the 2-mile tunnel, running in pitch darkness between 11pm and 5am and in low-level lighting at other times. The 55-hour time limit is non-negotiable. Extremely low-key and no-nonsense. Minimum qualifier of one 100-mile finish required. Organised by Cockbain Events.