Afghanistan is a landlocked country in Central-Asia. It has long borders with Iran and Pakistan. It borders on three of the new Central Asian republics: Kyrgyzstan, Uzbekistan, and Tajikstan. It has a very short border with China which is the result of a strange 19-th century Anglo-Russian deal.
Afghanistan used to be quite a popular travel destination in the 70's when hippies would go overland to India. The capital Kabul was a popular hangout, back then. Things have changed big time since then.

It started in 1979 when Afghanistan was invaded and occupied by the Soviet Union. The USSR was forced to withdraw 10 years later by anti-communist mujahidin forces supplied and trained by the US, Saudi Arabia, Pakistan, and others.

Fighting subsequently continued among the various mujahidin factions, but the fundamentalist Islamic Taliban movement has been able to seize most of the country. In addition to the continuing civil strife, the country suffers from enormous poverty, a crumbling infrastructure, and widespread live mines.

This means that you have to be brave in order to venture into Aghanistan. Tourists are not particularly welcome. For the adventurous, who have their mind set on going there, the most sensible thing to do might be crossing the Khyber Pass from Pakistan and move on to Jalalabad. (Note-while the city of Jalalabad is fairly safe, the border area is Taliban country.) You are on the road to Kabul now, but it may be an idea to turn back.... It should be noted that attacks on foreigners have increased dramatically since 2003 and it would be highly unwise for foreigners to travel without an armed escort. The safest way to visit Afghanistan is to fly into Kabul and travel by air to major cities once in country.

Travel outside of cities is not advised, and even major cities in the South and East should be avoided. Many of the major cities, including Kabul, Mazar-i-Sharif and others in the North and West are relatively safe for visitors. Kabul has several good restaurants and clubs that cater to expats and violence against foreigners is rare.

Another option might be to come from Uzbekistan and convince a cabby to take you from Termez to Mazar-i-sharif (do visit the ruins in Balkh when you are there - and back in a day. I haven't heard recent reports of anyone doing it, but did discuss it with a cab-driver in Samarkand. He was willing but expensive.

Herat, close to the Iranian border, has always been a relatively relaxed place for travelers. Though Irano-Afghan relationship dropped to an all-time low, it is possible to cross the border here. Valid passports and visas are required, though a visit to the State of Israel will prevent you from entering Iran.