Central Asia has opened up considerably since Uzbekistan and Kyrgyzstan dropped visa requirements for many nationalities. Those two countries carry most itineraries, and they complement each other: one for heritage, the other for mountains.
Uzbekistan lines up the Silk Road cities, Samarkand, Bukhara and Khiva, connected by fast trains that make the circuit straightforward in about ten days. Blue-tiled madrasas are the recurring motif, and the whole route can be travelled without particular logistical difficulty.
Kyrgyzstan does the opposite: few monuments, mountains everywhere. Treks around Song-Kol lake and the Tian Shan are done staying in yurts, and the country remains one of the cheapest on the continent, from about thirty euros a day. Kazakhstan, Tajikistan and Turkmenistan round out the group, the last being markedly harder to reach. The useful season runs May to September, after which the high passes close.