It's been raining at Gunung Padang, and the grass on the mountain's precipitous eastern slope is slick with water and mud.

But geologist Danny Hilman, is undeterred. While others slip and fall around him, he trudges expertly down this hill tucked away among the volcanoes 120 kilometres south of Jakarta to show off two big holes he's dug.

Since Dutch colonists discovered it in 1914, Gunung Padang has been known (though not widely) as the largest of a number of ancient megalithic sites in Indonesia....