Top Gear sets out on perhaps its toughest road trip ever - a high-altitude voyage from Kathmandu, capital of Nepal, to the Forbidden City 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 Top Gear presenters battle river crossings, mudslides and dizzying mountain passes on a trip that would test even the hardiest new 4x4s on the planet to the limit. But Paddy, Freddie and Chris aren't crossing the Himalayas in new 4x4s. They are crossing the Himalayas in a very small old Peugeot, a very small old Renault and Nepal's first (and only) home-built car.