Kathmandu is one of the most intense cities you can visit — a crowded, chaotic, endlessly fascinating capital pressed into a valley at 1,400 metres elevation, ringed by hills, and surrounded by some of the highest mountains on earth. The pollution is real and the traffic is maddening, but beneath the noise is a city of extraordinary antiquity and religious depth, where UNESCO World Heritage temples sit in living neighbourhoods, sadhus meander between modern shops, and the smell of incense competes with diesel fumes at every corner.
The heart of the old city is Durbar Square, a royal square packed with medieval pagoda temples, the old palace complex of Hanuman Dhoka, and the house of the Kumari — the living goddess who occasionally appears in an upper window while crowds watch silently below. Swayambhunath, the monkey temple on its hilltop west of the city, offers the best panoramic view and an introduction to the Newar Buddhist tradition. Boudhanath, the great stupa east of the centre, is one of the largest in the world — a serene place to walk the circumambulation path with pilgrims spinning prayer wheels. Pashupatinath on the banks of the Bagmati River is the most sacred Hindu temple in Nepal, and the open-air cremation ghats there are a confronting but important thing to witness.
The Thamel neighbourhood is where most travellers base themselves — a dense grid of guesthouses, trekking agencies, restaurants, and outdoor gear shops that can feel like a bubble, but which also has genuine character after dark. Asan Tol market, a few minutes' walk into the old city, is the commercial heart of Kathmandu's Newar community and one of the most alive places in the city. Patan, technically a separate city to the south but effectively merged into the Kathmandu urban area, has its own Durbar Square and an old town that many find even more atmospheric than Kathmandu's.
The valley is also the gateway to everything in Nepal: Everest base camp treks, the Annapurna circuit, Chitwan National Park, the ancient cities of Bhaktapur and Patan. Most visitors spend two or three days here before or after a trek, but Kathmandu is rich enough that a week is not too long.