The Semnan Citadel Gate, or Darvazeh-ye Arg, is the city's most recognisable monument: a compact Qajar gateway with blue tilework, small turrets, and a surprisingly dramatic decorative face. The rest of the citadel walls are gone, which makes the gate feel a little stranded in modern traffic, but it still has presence.
Look closely at the tile panels before moving on. The Rostam scene gives the building a flash of epic theatre, while the brick and tile details show how even a utilitarian city gate could become a civic emblem. It is a quick visit, but an essential one in Semnan.