Nepal has attracted trekkers from around the world since the 1960s when Col Jimmy Robert's organized the first commercial trek. Trekking has been the leading activity of tourists in Nepal and thousands take to the Himalayas, some doing a few days of hiking while others take on a month long trek through valleys and high mountain passes. Two of the most popular trekking regions are the Everest and Annapurna where many different trails can be followed while the other popular treks are in the Langtang and Kanchenjunga regions. The most challenging is the Great Himalayan Trails, an extensive trail system that covers Nepal from Humla and Darchula in the west to Kanchenjunga in the east. The diversity of trekking trails in Nepal cannot be found in any other part of the world. In fact, the lowest point in Nepal is 59 m above sea-level in the Tarai region while the highest point is Everest, 8,848 m above sea-level, the two points being only 200 kilometres apart as the crow flies.