In the burning desert north of this ancient Iranian city, the the Islamic republic's last followers of the Zoroastrian religion are making their annual pilgrimage to the temple of Chak-Chak.
"We are a species on the road to extinction," laments Babak, a man in his sixties who came from Tehran with his wife for the annual pilgrimage to one of the Zoroastrians' holiest sites - the rocky peak of Chak-Chak.
The site is a 70-kilometre drive from the central Iranian city of Yazd, the historical capital of what many consider to be the world's first monotheistic religion.
From the foot of towering rocks, pilgrims make their way up hundreds of steps to a cave to pray and drink clear water from a spring.
"This grotto is a historic site for us. After the invasion of the Arabs 1 400 years ago, King Yazdgerd III escaped to this desert," recounts Ghoshtasb Belivani, head of the Zoroastrian association at Sharifabad, the nearest town.
Yazdgerd III was the last Sassanian king, and last leader of the nation before Islam was imposed as its official religion.
"He was arrested at the same time as his first daughter. They were taken to Arabia. Nikbanou, his second daughter, took refuge in the grotto to escape the invaders," Belivani explained.
"After she cried and prayed, the mountain opened up and Nikbanou entered, and the mountain closed behind her. Since then, pure water has been pouring, drop by drop, from these rocks."
Legend also has it that a petrified colourful cloth from Nikbanou was also visible in the rocks, although pilgrims eventually took this.
"It may just be folklore, but it is undeniable that somebody important or a group of Zoroastrians took refuge here," added Kasra Vafadari, a respected member of the community and a teacher of history at the University of Nanterre, France.
Furthermore, scholars point out that the route was used in following centuries for Zoroastrians fleeing Iran - or Persia as it was formerly known - to escape religious persecution.
Once inside the grotto, women shrouded in white cast off their veils - obligatory in Islamic Iran - and drink tea and wine, which is permitted for religious use by non-Muslims in the Islamic republic.
They also read the Avesta, their sacred book, and light candles and incense. The annual pilgrimage, one of the highlights of the Zoroastrian calendar, lasts just 10 days.
Along with Judaism and Christianity, Zoroastrianism is a recognised - and therefore permitted - religion in Iran, where officially 99 percent of the 66 million-strong population are Muslims.
The religion was founded by Zarathustra - known to the Greeks as Zoroaster - a Persian prophet who believed he had seen visions of a God he called Ahura Mazda. Historians believe he lived at least 600 years BC.
Zoroastrianism was also dualistic - with God having an opponent, Aura Mainyu.
Zarathustra taught that humans are free to choose between right and wrong, truth and lie, and light and dark, and that their acts, words, and thoughts would affect their lives after death.
Their keeping of a sacred fire in their temples, symbolising light, led many to refer to them as "fire worshippers".
Many believe such precepts had a profound influence on Judaism, Christianity and Islam. Zoroastrianism also referred to an opposition between body and soul, a concept that is also central to the Islamic faith.
In a concession to their Persian roots and in contrast to many Sunni Muslim scholars, the Shi'a regime here recognises them as Kittabiyah - or people of the book and fellow monotheists as opposed to Kufr, or infidels.
But their numbers are declining sharply. Centuries of persecution have forced many to flee to India, where they are known as the Parsi and number between 80 000 and 100 000.
Discrimination in Iran continues today, for example in seeking employment in the state sector where Muslims are preferred.
Certain practices have also been outlawed. They no longer leave their dead on "towers of silence" to be devoured by vultures and not pollute the earth.
And ironically, the faith has also fallen victims to its own laws, notably the strict laws limiting their prospects of marriage to within their own community.
"Before the (1979 Islamic) revolution, there were more than 48 000 Zoroastrians. But today there are maybe 22 000, even though the population of Iran has doubled," Vafadari said.
"People are leaving because they have no future here."