Nowadays, permits are not issued to the visitors for Khyber pass, due to volatile safety situation in the area.

To enter the Khyber Pass you first need to obtain a permit from the Khyber political agency. Getting a permit can depend on the current political climate as they are not always available to tourists. In theory you should be able to get one on the same day - though that might involve greasing the palms of the official on duty. You also need an armed escort and transport. I believe tourists can organise to travel in groups. Personally I went in a taxi (which is not unaffordable), along with an Afridi guard armed with an AK47. The Khyber journey is great, though I do think this partly has something to do with the whole idea of the Pass as much as the actual views and landscape. It is fairly barren and, although interesting to see, I don't think it would be so much of a draw were it not for the element of adventure and possible danger associated with it. You travel past the Jamrud Fort, Ali Masjid, and the town of Landi Kotal before reaching the Michni checkpost. This is as far as tourists (or people without a visa for Afghanistan) can go. The next point is Torkham which is the border crossing. There is a train that goes the Khyber route though I'm not sure if it is still functional.

Enter and proceed through the pass