showing me through the labyrinth is pham thach. >> pham thach: be careful.z to work as a guide. >> anthony: how did they dispose of all of this earth and rock without revealing the tunnels? >> pham thach: the craters. you know, craters were everywhere on the like the landscape on the moon. >> anthony: right. >> pham thach: and you know the dirt of the craters all so fresh, look new. so they don't need to hide it, just leave them there. >> anthony: this was the maternity ward were thanh was born. and where did people sleep? >> pham thach: they have sleeping places, just holes like this, but smaller. two square meters only. >> anthony: right. >> pham thach: just enough to put a bamboo bed. >> anthony: how long did it take to build? >> pham thach: 20 months digging. >> anthony: 20 months of digging. >> pham thach: by hand. >> anthony: by handle. >> pham thach: with shovels and hoes and all up, you know, the farmers, they dug with with their tools. >> anthony: right. >> pham thach: under the bombing. >> anthony: while the bombing's going on they're down here dig