The Annapurna Circuit is one of the classic treks in the world and on the 'must do' list of any serious trekker or adventurer.  The circuit takes one around the Annapurna Himal, following the courses of 2 mighty rivers: the Marsyangdi in the east and the Kaligandaki in the west, and takes one over the 5400m-high Thorung La Pass in between the upper reaches of the rivers. The Kaligandaki is the world's deepest gorge, flanked by the giant Dhaulagiri and Annapurna Himals. The flora, geography and culture also change dramatically around the circuit.