Mike Bushell takes on the Tough Guy event
28 January 2012 Last updated at 19:29 GMT
This weekend, more than 5,000 people will - willingly - crawl through dark muddy tunnels, jump into freezing cold water and climb over mountainous obstacles.
On the way up and down, they will probably get electric shocks and generally experience tear-inducing fear and pain.
It is all in the name of the annual January Tough Guy event which has been going for 25 years.
The BBC's Mike Bushell went to find out what the appeal could possibly be.
Featured in the report are Tough Guy creator Mr Mouse, headteacher John Smith, Tough Mudder creator Will Dean and British best challenger Ben Kirkup.