Which Ultramarathon Requires the Most Mental Toughness?

With a length of 208 miles, the Tunnel Ultra isn't the world's longest ultramarathon, but it's hard to imagine a more psychologically demanding running event. The course design is deceptively simple: participants run the length of the Combe Down Tunnel, the UK's longest cycling tunnel, located just outside of Bath, England. When a runner reaches the end of the tunnel (slightly longer than a mile), they turn around. To finish the race, you must complete 200 lengths (out-and-back 100 times). For experienced ultramarathoners, that should be simple, right?

Not exactly. Though the format is straightforward, the race is designed to push participants to the limits of what they can handle, both physically and mentally. On the plus side, you don’t have to worry about navigation, bad weather, or carrying many supplies. On the other hand, you’re doing a shuttle run in a dimly lit tunnel (with no lights between 11 pm and 5 am). You're not allowed to run alongside anyone else or use headphones.

There's also a strict time limit of 55 hours. Runners are allowed to sit down or even sleep in between laps, but many choose not to, worrying that they will lose their drive to finish or waste valuable time. A small table at the entrance to the tunnel serves as race HQ – and provides a tempting place to throw in the towel at the end of each lap for runners who have had enough. A speaker blaring classical music halfway along the tunnel provides another form of mental torture. Many participants have experienced vivid hallucinations that lasted long after the race finished – and at least one person temporarily went blind.

"A mind-bending test of extreme endurance and sensory deprivation":