Na'in is an old desert town between Isfahan and Yazd, close enough to the main route that it is easy to miss and good enough that you should not. Its historic quarter holds one of Iran's oldest mosques, a ruined pre-Islamic castle, traditional houses, a bazaar, and traces of the qanat system that made settlement here possible.
The Jameh Mosque is the reason to stop. Its brick arcades, carved stucco, basement, and early minaret feel far older and more austere than the blue-tiled mosques of Isfahan. Across from it, the Pirnia Traditional House shows the domestic side of desert architecture.
Na'in is also known for fine carpets, often in pale blue and cream. You do not need a full day here unless you are deep into architecture, but as a break between Isfahan and Yazd it is far more rewarding than another roadside tea stop.