Xi'an was the capital of China for eleven dynasties and the eastern terminus of the Silk Road. The headline sight is of course the Terracotta Warriors, 40 km east of the city, but the historic core itself rewards two or three days of slow exploration.
Inside the Ming-era city walls — best ridden by rented bicycle around the full 14-km circuit — the Bell Tower and Drum Tower mark the geographic centre, and the Muslim Quarter immediately to their west is the city's beating heart for food and atmosphere. The Stele Forest on Shuyuanmen is the city's most underrated museum.
South of the walls, the Tang dynasty pagodas at the Big Wild Goose and Small Wild Goose temples mark the Tang capital's old precincts, and the nearby Shaanxi History Museum is one of the great museums of China. Allow a full day for the warriors, a half day for the Stele Forest and city walls, a half day for the Muslim Quarter and the towers, and a full day for the south-of-walls museum-and-pagoda district.