Top Gear sets out on perhaps its toughest road trip ever - a high-altitude voyage from Kathmandu, capital of Nepal, to the Forbidden Ci ty of Lo Manthang, a secretive kingdom perched high on the Tibetan plateau, on the far side of the Himalayas. It is a five-day expedition through the highest mountains, deepest gorges and harshest terrain on the planet. On their journey, the To...