I'm sharing a wonderfully informative email by Alan Casey, an Irishman I met in Korea. He is married to an Iranian.
As for things to do and places to see in Tehran, I would recommend the following: - Golestan Palace in the middle of Tehan. This was the palace of the ruling Qajar dynasty which ruled Iran around the end of the 19th century immediately before the Pahlavis came to power. - the Pahlavi (ie. the Shahs) palaces in the north of Tehran, namely Nievarand and Sadabad. Interestingly for me anyway, the mullahs have retained these monuments to decadence and opulence as tourist sites for the public. You can see rooms where the Shah hosted foreign heads of state such as Nixon, the Queen, et al. Enjoy a non-alcoholic beer in the grounds of Nievarand! - the main Bazaar in the middle of Tehran, close to Golestan Palace. Has to be seen to be believed. - the mosque right beside the bazaar. Not as spectacular as the mosques of Isfahan, but worth seeing nonetheless. - the house where Khomeini lived. Was interesting for me anyway - a very modest little house in the north of Tehran. - Bobby Sands street near the British Embassy, if you know your Irish history.. - the compound where the US embassy used to be - not much to see here, but maybe if you recall the hostage crisis, then you might want to see it. - outdoor restaurants in the north of Tehran in the foothills of the mountains. Great place to sit and seat and watch the world go by. Places I haven't been to in Tehran but which might be worth seeing are: - the mausoleum of Khomeini to the south of Tehran on the way to the new airport, called, surprise, surprise, Imaam Khomeini international airport! - jewelly museum, we meant to go and see it once, but we hadn't time. - Azadi tower built by the Shah. It's one of the more recognizable landmarks in Tehran. As for general info, remember that you can't wear shorts in Tehran. Sandals are fine though. Booze while illegal, can be obtained relatively easily if you in the company of Iranians. The Armenians normally supply the booze. Basically it's like ringing for a take-away when you order booze. Try and sample the local vodka, arak. You can get anything you want - the government are probably secretly siphoning off their cut from the importation of booze - it's all a bit of a sham really.