The Vieng Xai caves, in Hua Phan province, were used by the Pathet Lao, during the Vietnam war. In these caves, they were relatively safe for the heavy bombardments, conducted by the Americans in Laos.

It is a collection of about 100 caves, which are difficult to reach and sometimes even difficult to see. It gave shelter to 23,000 people, and there was a hospital with an operating theatre. But there were also schools, factories, sports areas and even a nightclub. Some of the rooms could be made airtight, so that a gas attack could be survived.

After the war the caves were used as re-education camps for about 40,000 officials and soldiers of the former government. Among them was King Savang Vatthana, who died in the caves.

Since 1997 the complex is open to visitors. The Lao government is hoping to turn this place into a tourist attraction, something like the Cu Chi tunnels near Ho Chi Minh city, in Vietnam.

• Visit Viengxay website