That is a qanat, and Zarch, east of Yazd, has one of the most famous in Iran, often described as among the longest in the world. Its main channel is dug by hand through the ground, with a line of vertical shafts every few dozen metres so that the diggers could haul up spoil and let in air. From the surface the shafts look like a row of craters running across the plain.
The qanat is the reason Yazd exists at all. The city lies on the edge of two great deserts, the Dasht-e Kavir and the Dasht-e Lut, and it gets almost no rain, yet it has grown for centuries on water that arrived through these tunnels. The old city is built of sun-dried mud brick, with wind towers rising from the roofs to catch and cool the air, and the old Zoroastrian community still lives here, keeping fire temples and the tradition of the Towers of Silence on the hills outside. In 2016 a group of eleven qanats, Zarch's neighbour among them, were listed together as a World Heritage property.
On a motorcycle this is desert riding of the classic kind. The highways around Yazd are broad, flat and straight, with long views, a hard sun and very little shade, and the hours between noon and four are better spent in a courtyard teahouse than on the asphalt. Spring and autumn are the good seasons; in midsummer the heat can be brutal, and winter nights are cold. Wind can pick up dust, so goggles or a closed visor are worth having. A short drive south-east the mud-brick village of Kharanaq, partly abandoned and partly restored, makes a good detour.
Yazd itself is a big, calm city, and it has fuel, food and a famous sweet shop tradition. Nothing at the qanat itself will serve you, so fill the tank and carry water before you go. Dress modestly and be ready for a conversation in broken English, because people here tend to be curious and generous with their time and their tea.