Dr Howard and his wife Dr Deb spend most of their time on cave expeditions. Howard has been exploring caves in the UK and Europe since he was 15.

The limestone karst mountains were so attractive that they decided to go to Asia in 1990. The couple patiently sought the cooperation of regional agencies and organizations. Finally, they got some help from Hanoi General University, now named Hanoi National University, to make their trip to Vietnam possible.

After that, they focused on exploring destinations in Vietnam. Being a member of the British Cave Research Association, Howard has led an expedition team on trips to Vietnam since 1990.

The team has cooperated with Hanoi National University to conduct 14 journeys to different localities in Vietnam, including Quang Binh, Nghe An, Thanh Hoa, Hoa Binh, Lang Son, Cao Bang and Ha Giang. It has discovered nearly 300km of caves in Vietnam.

In 1997, the team found Khe Ry in Quang Binh Province, the world's longest underground cave. In 2009, it discovered Son Doong, the world's biggest cave, also in Quang Binh.

Their reports have contributed to Phong Nha-Ke Bang National Park being recognized by UNESCO as a World Natural Heritage Site.

According to Dr Howard, Vietnam has one of the world's most impressive limestone areas. Clearly, many caves situated in Ke Bang Mountain have yet to be found, Howard and his team hope to continue their search with the cooperation of the Vietnam National University, Hanoi.

The couple has helped call on the international community to pay attention to the protection of Vietnam's nature and environment. They have also shown a number of well-known film crews around Vietnam.

Through the films, the world has become more aware of Vietnam's beauty and the world's biggest cave, Son Doong, in Quang Binh

The couple plan to visit Vietnam again from March 3 to April 26, 2012, along with their team and some film crews to make documentaries about caves in Quang Binh.

In 2010, the British expedition team took the film crews and reporters from Kyodo, NHK, BBC, and National Geographic among others, to Vietnam to shoot films about Son Doong Cave. In 2011, they invited representatives from the BBC to Quang Binh to make another film about Son Doong Cave.