The Xi'an Metro is the easiest way to move around the modern city. The most useful lines for travellers are Line 1 (east–west under the city, from the railway station via the Bell Tower to the West Gate area) and Line 2 (north–south through the Bell Tower, connecting Xi'an North high-speed rail station to the south of the city). Trains run roughly 6am to 11pm; signage is bilingual.
Inside the city walls, the easiest way to see the historic core is on foot or by bicycle. You can rent a bike on top of the City Walls for the wall circuit (about two hours for the full 14 km), and bike-share apps work throughout the centre.
For sights outside the walls — Big Wild Goose Pagoda, Shaanxi History Museum — taxis are cheap and plentiful, but ride-hailing apps (Didi) are usually quicker than flagging one down. For the Terracotta Warriors, Huaqing Pool, and Lintong, the easiest option is the dedicated tourist bus 5(306) from the east square of Xi'an railway station; it costs less than a taxi and stops at all three.