Bukhara's old city is one of the most concentrated collections of medieval Islamic architecture in the world. Nearly everything worth seeing is walkable from Lab-i-Hauz, the teahouse square at the heart of the historic centre.
Start at the Po-i-Kalyan complex — the Kalyan Minaret, the Kalan Mosque, and the Mir-i-Arab Madrasah make up the most important architectural ensemble in the city. From there walk north to the Ulugbek and Abdulaziz Khan Madrasahs, where you can browse craft workshops inside working medieval buildings. The domed bazaars connect this district to the Lab-i-Hauz area.
West of the Lab-i-Hauz is the Ark, the massive mud-brick citadel, with Bolo Haouz Mosque facing it across the plaza and the Zindon prison tucked alongside. In the park beyond the Ark you'll find the Samanid Mausoleum — the oldest surviving building in the city — and the Chashma-Ayub Mausoleum with its sacred spring.
For something off the main circuit, the Saif ed-Din Bokharzi Mausoleums in the eastern Faroband district are beautiful and rarely crowded. The Magok-i-Attari Mosque — buried several metres below current street level — is the oldest mosque in Bukhara and houses a good textile museum. A taxi ride north of the city brings you to Sitorai Mokhi-Khosa, the last emir's summer palace, now a fascinating museum of the twilight years of the emirate.