Suleiman natural prison, Takab, Iran
Used to be a Zoroastrian praying siteZendane Soleiman, or Soleiman Jail, is indeed a geological structure; remnants of a dried karstic spring. Similar active hot springs are still there around the old dried one, and also one most important of all, inside the Takhte Soleiman UNESCO world heritage site. In the local legends, king Soleiman had imprisoned devils in the well like dried spring. The creator is still open, accessible by about 10 min hiking. When you arrive at the top, it is really breath taking to watch down. There are also haundrads of birds, mostly swallows nesting inside the well. It's view to the plain bellow and the main Takhte Soleiman is also amazing.
This is a hugely impressive site with an amazing history. It stands out from the landscape amazingly. I managed to climb three quarters of the way up, but found it too steep and difficult to reach the top and so was hugely disappointed. My husband and our guide got to the top and told me about the wonderful, deep pit at the top. Most people would manage the ascent.