Yeah, Turkmenistan was a pain in the arse. When you apply for the transit visa you will be asked for the intended route. I made the mistake on mentioning Darvaza where the gas creator is as a via point and my transit visa was denied. But in fairness a staff member in the Turkmenistan Embassy in London told me to apply again but only to mention the entry and exit points. So I reapplied to London and they duly sent my application back again to be processed in Turkmenistan and finally I got the "letter of permission" just a few days before I reached the Turkmen border. If it was to be refused a second time then I would have had to make a u-turn in Iran and would have had it all to do to get back to Armenia before my Iranian visa expired - the joys of travel!
Another thing to note is that whilst the "letter of permission" stated 5 days, as I had indicated on my application form, the young pup of an immigration boy decided 3 days would be enough. He presented me with an official document that had a rudimentary map of Turkmenistan on it and he marked the route that I must follow and dictated the places that I would stay each night - which ironically included Darvaza. But I played his game and told him he was a great boy and soon after I found myself riding towards Ashgabat! I was stopped by the police during the transit, which I actually did in 2 days and they checked my document to ensure I was on the intended route. Otherwise I found Turkmenistan to be an interesting but weird place with nice people.

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