This is the playground of the capital. On Fridays, when the Iranian weekend begins, the roads fill with families heading up to cool valleys, streams and picnic spots under the walnut trees.
The Alborz are young, steep mountains, the highest of them capped by Damavand, a volcanic cone that on clear days stands white above everything. Here the valleys are narrower and greener than anything on the dry plateau to the south, with orchards in the bottoms, shepherds' huts on the slopes and old stone villages built for protection. A fortification in the name of the site, Qosṭinlār, points to how long people have been guarding passes in this region, because routes across the range were always strategic, whether for armies, merchants or pilgrims.
For riding, the main mountain roads through this area are among the best in Iran: long climbs, hairpins, tunnels and big drops, with a lot of truck and weekend traffic on the busiest routes. Go midweek if you can, start early and expect cold at the top even in summer, because passes in the Alborz sit well above two thousand metres and weather turns fast, with fog, rain and occasional snow outside the warm months. Surfaces vary, so watch for potholes and gravel on the corners after a thaw or a storm.
Karaj, a big city, is the sensible place to fill up, and small villages along the way will have little more than a shop or a tea house. Carry water, keep fuel above half and plan lunch in a village, because a plate of grilled fish or kebab and a pot of tea are the standard mountain refuel.
The best months are May, June and September to early October, when snow has gone from the lower slopes and the days are warm. Winter means closures and ice on high stretches, so check the road before committing.