Central Asia's holiest city, Bukhara (on road signs you'll see the Latinised Uzbek word Buxoro, pronounced Buhoro) has buildings spanning a thousand years of history, and a thoroughly lived-in old centre that probably hasn't changed much in two centuries. It is one of the best places in Central Asia for a glimpse of pre-Russian Turkestan.
Most of the centre is an architectural preserve, full of former medressas, a massive royal fortress, and the remnants of a once-vast market complex. Allow at least two days to look around. If you're short on time, at least see Lyabi-Hauz, the covered markets, the Kalon Minaret and Mosque, the mausoleum of Ismail Samani and the unique little Char Minar.