The Annapurna Conservation Area is Nepal's largest protected area, and no other region packs so much into one trip. In a few days you walk from terraced Gurung villages through rhododendron forest into the Annapurna Sanctuary, a ring of peaks above 7,000 m with Annapurna I (8,091 m) at its head.
On the far side of the range, the Annapurna Circuit crosses Thorong La (5,416 m) into the dry, Tibetan-style landscape of Manang and Mustang and down to the temple at Muktinath. Every route starts from Pokhara, and the teahouses are the most comfortable in the Himalaya.
Short on time? The Poon Hill trek gives you a sunrise over Dhaulagiri and Annapurna South in four or five days.