If you're into religious history, the Blue Mosque in Mazar-e-Sharif is one of a few reputed burial sites for Ali, Mohammed's cousin and son-in-law (there's a lot of that). If the history's important to you, the Wikipedia page for it is probably accurate enough.
I like it for the gorgeous, reconstructed tiles in several shades of blue (and other colors). From a distance, all you see is the blue. Up close, you see a) all the colors and b) the intricacy of the tile work. Should you happen to be traveling through Central Asia, and have a chance to visit, it's well worth it.