Question: I am wondering whether there is a train from Istanbul to Tehran or whether there's a bus from Damascus for the same destination. I plan on getting either a tourist visa or, if at all possible, a pilgrimage visa b/c I am a photographer and am planning the Iran visit in order to photograph the great historic mosques and madrassahs.
Answer: Once a week there is train form Istanbul to Tehran every Wednesday night around 10 - 11pm. For more details about the trains you can check: http://www.uppersia.com/Iran-transport-services/iran-train-ticket-booking-service.html
You can also take a bus from Istanbul to Tabriz (30 hours) or continue to Tehran (40 hours) which costs about $30.
Fill in the visa form on http://www.uppersia.com/Iran-travel-services/iran-visa.html, it takes about 10 working days to get your reference number and two working days to collect your visa at the embassy by direct referral or one working week by posting the docs to the embassy. You can pay the visa fee in cash in Iran.
Check the cheapest Iran tours at http://www.uppersia.com/Iran-tours