Shahmirzad is a mountain town about 10 kilometres northwest of Mahdishar, set at a slightly higher elevation on the southern Alborz slopes. In summer the population swells from a few thousand to close to 40,000 as city dwellers from Semnan and Tehran come for the cool air, the shade of the gardens, and the famous tree-lined lanes. The contrast with the heat of the plateau is immediate and dramatic — temperatures here can be 10–15°C cooler than Semnan, which sits at a lower elevation only 24 kilometres away.
The main reason to come is the landscape and the slow pace. The 700-hectare walnut orchard to the east of town is the world's largest, according to the FAO, and a walk or drive through it in late summer — when the walnuts are ripening — is genuinely pleasant. The town also produces Tenab-e Shahmirzad, a mineral water bottled from local springs. Historically, Shahmirzad served as a summer retreat for Qajar royalty and nobility; some older mansions survive in varying states of repair.