You may be tempted to see a lot during your visit to Iran, but this city on the Silk road deserves your attention and you may want to stay more. I did… In the limits of the desert, old Yazd was built with adobe during the Qajar era. Most of the adobe traditional dwellings are dominated by badgirs, or wind towers: a simple and efficient way to make air circulate inside the houses producing an astonishing breeze for the house, a natural airconditioning. The old centre is full of such houses, nowadays preserved, restored and put to touristic use as  enticing boutique hotels for your 1001 nights, sipping tea and watching the starry sky.
The most important thing to see in Yazd are by far the Towers of silence, where dead people were once brought to be eaten by vultures. Centuries after the scenery is still eerie and visiting the place leaves one with as strange feeling of  silence indeed, and futility for all other matters.
The city is also the centre of one of the most strange religions that exist: Zoroastrianism. But equally impressive is the zurkaneh, the house of strength and the gentlemen (javah mard) practising an ancient sport of lifting and turning heavy wooden clubs to build muscles under the sound of music. The sport is taking place in Yazd in a former water tower (Saheb A Zaman Zurjaneh) with five badgirs that will help you not boil from the heat.
Do not forget to visit a traditional house (khan-e sonnati) transformed into a hotel, be it even for a tea. Rest your tired body beside a water fountain and lull yourself to a thousand year old sleep!