Yanar Dag, also known as Burning Mountain, is a natural gas fire which blazes continuously on a hillside on the Absheron Peninsula on the Caspian Sea near Baku, the capital of Azerbaijan. A unique natural phenomenon due to a steady seep of natural gas from the subsurface, it is considered to have been burning for thousands of years. Flames jet out into the air 3 metres from a thin, porous sandstone layer. Historically, this place has been considered sacred by Zoroastrians and other fire worshippers. The natural eternal flame became a tourist attraction, with visitors coming to see this unusual spectacle on the Silk Road. The area surrounding Yanar Dag is a natural reserve protected by the state. The flames can be observed leaping into the air from a distance, giving the mountain a mystical and otherworldly ambiance particularly powerful at night. The mountain lacks any visible seepage of liquid fuel, suggesting a purely gas-based source. This natural fire has been burning for centuries due to the large concentrations of natural gas in the area.