You may be surprised to learn that it is not all that difficult to travel from London, Paris or almost any other big European city to Tehran by train. All you need to do is to get to Istanbul. From there you can travel farther east, across Turkey to Iran.
Or else, just start in Istanbul and do the Turkish section of the trip. Rather than go through the process step by step here is a link to a terrific website all about train travel, and to the page on that website that tells you how to travel to Iran by train.
http://www.seat61.com/Iran.htm#.VGqAaPnF-So
Once you get to Iran, whether it is by train or by plane, you can travel all over the country by train. The trouble is that almost all the long-distance trains run at night, so you don’t get a chance to see much of the scenery. If that doesn’t bother you and you like trains, then Iran is a good train country.
You will still have to travel within Iran with a guide accompanying you. So if you do want to travel by train inside Iran, get in touch with us and let us arrange it for you.