The purpose of the expedition was to study the Hang Khe Rhy cave,one of the longest caves ih Southest Asia. They also wanted to measure the length of the soon Trach river,which flows through the cave. The cave is deep in the jungle in Vietnam's Quang Binh province. The area around the cave is home to a great variety of rare flora and fauna. Peter and fifteen other experts had been asked to study this area by the Vietnamese government.