I took this photo as I entered the cave (sanctuary) at Marble Mountain (Vietnamese: Ngũ Hành Sơn; "Five elements mountains"). I wanted shots without people - this is a popular site just outside the coastal city of DaNang, so that was not an easy thing to accomplish.
During the American war I spent 10 months in and around DaNang and had no idea the caves existed - another example of me being clueless about Vietnam when I was 19. Apparently the National Liberation Front (Vietcong) new about the caves and made good use of them.