The most famous of the caves, Tham Jang, was used as a bunker in defence against marauding jęen hór (Yunnanese Chinese) in the early 19th century (jąng means ‘steadfast’). Stairs lead up to the main cavern entrance.
Read more: http://www.lonelyplanet.com/laos/northern-laos/vang-vieng/sights/natural-landmarks/tham-jang#ixzz3ra8V1cjX