Ajina-Tepe (meaning "devil's hill" in Tajik — locals gave it the name without knowing what it was) is the site of a 7th–8th century Buddhist monastery complex, 12 kilometres east of Bokhtar. The monastery was active during a period when Buddhism was flourishing in the Sogdian and Bactrian regions of what is now Tajikistan and Uzbekistan, before the Arab conquest brought the religion to an abrupt end.
Soviet archaeological excavations in the 1960s uncovered a double-monastery complex — one half for monks, one half as a temple — with remarkably well-preserved remains of wall paintings, clay sculptures, and architectural decoration. The jewel of the find was a 13-metre reclining Buddha figure, found in thousands of fragments. The reassembled statue is now in the National Museum of Antiquities of Tajikistan in Dushanbe, and is one of the most important Buddhist artworks in the world.
The site itself today is an extensive mound of excavated ruins with limited interpretation on the ground. A visit is more rewarding if you have read about the monastery and seen photographs of the artefacts beforehand. Getting there requires a taxi from Bokhtar; the road is reasonable.