The United Nations Educational, Scientific and Cultural Organization (UNESCO) seeks to encourage the identification, protection and preservation of cultural and natural heritage around the world considered to be of outstanding value to humanity.
There are over a thousand UNESCO World Heritage sites. (See map here with photos: http://whc.unesco.org/en/list/)
I have coloured the sites I have visited in blue in the map below. This list links to my geotagged photos of some of them: