Iran has a bad reputation, but it is not deserved. Iranians are really very friendly and the country is so rich, from a cultural perspective, that the fifteen days of stay the visa you can get at Tehran's airport will allow you will not be enough. Mosques, palaces, remains of the persian empire... architecture lovers will have plenty to visit. Finally, if you choose to do a few days of hiking in the Alborz or Zagros mountain ranges, you may find them average after such wonderful sights.
Check out the photos of the trek on Flickr, to download the images in their original size and see on a map the places where they were taken.