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The monsoon which sustains this lush and fertile valley

owes its very existence to the Tibetan plateau.

Like a giant hotplate, the plateau heats up in the spring and summer.

The change in air pressure

draws in warm moist air from the Indian Ocean in the south.

Thanks to this

Over a billion people from India to Burma

benefit from the monsoon rain that this wind brings with it.

Tibet is the engine that drives the fertility of a whole subcontinent.

But Tibet has an even greater role in the ecology of the region.

Clues to this function are found in a legend that pre-dates

even the ancient Tibetan culture

and which still draws pilgrims from all over the world.

Several world religions believe

in a mythical mountain that's equivalent to the Garden of Eden.

Its peak has four faces,aligned to the points of the compass

and from its summit four rivers are said to flow to the four quarters of the world.

Thanks to its life-giving waters

this mountain is known as the "axis of the world".

In one of the remotest areas of Tibet

there's a place where this legend takes physical form.

That place is Mount Kailash.