Zoroastrians are commonly thought of as fire worshippers. And they do worship in fire temples, such as Ateshgah, on the outskirts of Baku, capital of Azerbaijan, so it is easy enough to see how the misunderstanding came about.
However, it is not the case.

Photo credit: Benjamin White
Zoroastrians incorporate fire into their temples because they see fire as pure. Fire is pure because it’s an element that cannot be polluted. And it is through this pure medium that truth may be perceived and spiritual insight gained.
Most fire temples will have a fire altar upon which an eternal flame burns. This fire is symbolic of the light and wisdom of Ahura Mazda, the Zoroastrian deity.
Ateshgah – The Fire Temple of Baku

Photo credit: Amrita Ronnachit
Ateshgah, the fire temple of Baku, is thought to have been constructed between the 1600s and 1700s. The temple features a castle-like outer wall, a large courtyard, and a small altar containing the eternal flame.
The original eternal flame – which utilised a natural source of a gas – burned uninterrupted for centuries before going out in 1969. Nearby gas and oil extraction operations were blamed.
The new eternal flame relies on a gas pipe.

Photo credit: Amrita Ronnachit
Oil and gas is so plentiful on the Absheron Peninsula – home of Ateshgah – it seeps from the ground and bubbles to the surface unaided.
At nearby Yanar Dag, a natural gas vent burns with a three metre high flame. It’s been alight since at least the 1950s.

Photo credit: Benjamin White
Practical information and how to reach Ateshgah:
Ateshgah is located on the outskirts of the Azerbaijani capital and can easily be reached with public transport. More transport info here.
Ateshgah is on the tentative list for UNESCO World heritage listing.
More on Azerbaijan:
Baku – at 28m below sea level, it’s the world’s deepest capital
Gobustan – stone age petroglyphs that inspired Thor Heyerdahl
Mud volcanos, Gobustan – it’s the mud volcano capital
More on Zoroastrianism:
Chak Chak, Iran – holiest of holy sites for Zoroastrians
Dakhmeh-ye Zartoshtiyun, Yazd, Iran – Zoroastrian tower of silence
Takht-e Soleyman, Iran – royal Zoroastrian sanctuary and fire temple
Chilpik, Qaraqalpaqstan – Zoroastrian Tower of the Dead
Posts on the Caucasus:
Georgia:
Vardzia – 400 room, 19 level cave city. Watch out for falling rocks!
Ushguli – watchtowers on every house; even Genghis Khan was deterred
Nagorno-Karabakh:
Sea Stone Hotel, Vank – a lion head carved into the hillside. Pure genius!
Armenia:
The Temple of Garni – a much smaller Parthenon, built for the sun god Mihr
Zorats Karer – 223 standing stones in a grassy field. Is it linked to Stonehenge?