Chitgar Lake, also known as Persian Gulf Lake, is a large artificial lake in western Tehran. It gives the city a broad recreational waterfront, with promenades, cycling, boating, and views toward the Alborz when the air is clear.
It is far from Tehran's historic core, but that distance is part of the story: a newer leisure landscape for a huge, expanding metropolis. Go in the evening if you want to see it at its liveliest and avoid the harshest sun.