Stand beneath the dome of Soltaniyeh and look up. The inner surface rises in a great curve of brick and plaster, the proportions as calm as an egg, and the light falls from windows in the drum so that the whole interior seems to float. This is the mausoleum of Oljeitu, built between 1305 and 1313, and it is the oldest surviving double-shell dome in Persia. The outer shell is a tall, ribbed bulb covered in turquoise glaze, which once glittered across the plain like a jewel, and the inner shell is separated from it by a gap that kept the mass of the roof manageable. Around the base stand eight minarets, slender and decorated with tile, which have long since lost their tops.
The inside is much better than you expect from the plain exterior. In the main chamber, which is about twenty-five metres across, the walls carry stucco decoration of the Ilkhanid period, with Quranic inscriptions in Kufic script, and the traces of painted designs in red, blue and gold. An upper gallery wraps around the room, and the stairs lead up into the space between the shells, from which you can look down into the chamber and out over the plain. Parts of the structure have been strengthened after earthquakes, and visitors must obey the rules for what may be climbed and when.
Inside, sound behaves oddly. A voice in the middle of the floor echoes for several seconds, and a clap rings up into the dome, so people tend to speak in whispers. The interior is cool on a summer day and bitterly cold in winter, with a stone smell. A small museum in the lower crypt holds artefacts and photographs of the restoration, and the guards are often keen to show visitors the best views. Entry costs a modest fee, and foreigners pay more than locals.
The approach is simple, a short road from the highway, with a car park and a row of stalls selling tea, souvenirs and local sweets. Fuel is in Abhar or Zanjan, about thirty-six kilometres each way. Come in the morning if you can, because the light is better for photographs and the coaches have not arrived yet. If you can, return at sunset, when the dome turns copper and the plain turns violet, and the minarets stand out against a darkening sky.