You could do a whistlestop tour of the classic sights in eight to ten days. If you trek into the Annapurna region, you'll need another week or two – depending how far and how fast you walk.
The capital has boomed in recent years, becoming a busy, polluted, modern city, but it still preserves a stunning medieval heart and an easygoing restaurant and nightlife scene.
At the holy riverbank of Pashupatinath, the Hindu dead are cremated in the open; just down the road lies the dizzyingly exotic Tibetan Buddhist community of Boudha.
The stunningly preserved micro-city of Bhaktapur offers a taste of what Kathmandu was like before the modern world arrived.
Poised on a precipitous ridge, the old-world bazaar town of Bandipur has become an easygoing haven, packed with gorgeous boutique hotels and friendly homestay lodges.
Set under the white peaks of the Annapurna range, lakeside Pokhara is Nepal's biggest tourist centre. You can paraglide, meditate or just relax on a boat or in a bar.
The Annapurna range rises above some of Nepal's lushest, steepest and loveliest foothills – perfect for a shorter trek to the viewpoint of Poon Hill, or, with a few more days in hand, up to the uplifting Annapurna Sanctuary and then back to Pokhara.
From Pokhara, head off next to the jungle, grassland and rivers of Chitwan National Park. You're almost guaranteed sightings of rhinos, deer, monkeys, crocodiles and countless species of birds. You might not spot the elusive tigers, but you can ride on an elephant.