One of the world's most challenging races has thousands of people testing their mental and physical grit.
The Tough Mudder made the Lehigh Valley its home this weekend.
The first wave of brave souls challenged the course Saturday morning in Heidelberg Township, Lehigh County.
The 10-and-a-half mile obstacle course designed by British Special Forces had runners going through 22 obstacles filled with fire, ice, and electrified wires.
But runners say the biggest challenge is beating the heat.
"It's a little rough, its hot but last year I did it in 29 degrees so it's a big difference," said Elizabeth Dando of Ashlyn.
Another competitor only known as "Tough Timmy" shared the same views.
"The heat was really hard actually. There is minimal shade so it's a hard event. We did Mt. Snow last year and that was tough. But this is harder because you're in the middle of an open pasture with the sun beating down on you. It's tough but it's fun."
More than 15,000 runners conquered the course by the end of Sunday's festivities.