Nuristan is in the Northeast part of Afghanistan.
Nuristan is one of the most remote areas on Earth, right up in the Hindu Kush mountains. "Hindu Kush" translates as "Hindu Killer", which describes the terrain and climate well. The area used to be called Kafiristan, land of unbelievers, until it was converted to Islam at swordpoint in the 19th century and became known as Nuristan, land of light.
Kipling wrote of it in "The Man Who Would be King". In his day, no Europeans had been there. John Huston made a film  based on the book, with Sean Connery and Michael Caine in lead roles. It is a fine movie and the geography is about right, but the culture is more from Kipling's imagination than anything related to the actual place.
Another wonderful book about the area is Eric Newby's "A Short Walk in the Hindu Kush", long out of print but recently reprinted by Lonely Planet,  ISBN: 0864426046. When Newby and a friend visited Nuristan in the 1950s, they were the second or third European expedition ever to reach it.
kashi, how are you/ lesem, fine/ ow, water/ boodi, bread/ korangi, where are you going/
To even get close to Nuristan, you need a four-wheel drive vehicle with a winch and other rough-country preparation.
For most of the area, you need to hike or ride a horse or donkey. A local guide is near mandatory.
There are some peaks of interest to mountain climbers.
In addition to the warning box above, Nuristan poses risks of altitude sickness.