شمشک and دیزین
Not too far from North Tehran you can find great pistes for skiing during winter. Both Shemshak and Dizin are popular with rich Iranians and feature on many Instagram feeds. During summer the area is way cooler than the city, though there is not much in terms of lush vegetation. If you manage to be in Iran from the first snowfall to the end of the season, make sure you spend a weekend at either Shemshak or Dizin. The season in Iran lasts longer than in Europe because the altitudes are higher. There may be snow from November until May. You may think you are in the Alps, not the Alborz.
There are other resorts such as Tochal, Damavand and Abali. Have a look at Iran Ski Tours for more information.