challenge

A participant in the Mud Day event throws a bucket of mud at a friend during the Mud Day run in Beynes, west of Paris, Thursday, May 8, 2014. Thousands of runners seeking a challenge competed in a circuit of approximately 13 kilometers (8 miles) with over 20 obstacles, most of them set in mud.

Francois Mori/AP

A participant in the Mud Day event throws a bucket of mud at a friend during run in Beynes, west of Paris on Thursday. Thousands of runners seeking a challenge competed in a circuit of approximately 13 kilometers (8 miles) with over 20 obstacles, most of them set in mud.

Hot air balloons fly across Qiongzhou Strait in Haikou, south China's Hainan province during the H1 China Hot Air Balloon Challenge on June 18, 2013. Fifteen balloons flew over the strait in 2.5 hours and succeeded in landing on Leizhou Peninsula in Hai'an.

AFP

Hot air balloons fly across Qiongzhou Strait in Haikou, south China‘s Hainan province, as part of the H1 Hot Air Balloon Challenge on Tuesday. Fifteen balloons flew over the strait in 2.5 hours and succeeded in landing on Leizhou Peninsula