A World Heritage Site is a place (such as a building, city, complex, desert, forest, island, lake, monument, or mountain) that is listed by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as being of special cultural or physical significance. The list is maintained by the international World Heritage Programme administered by the UNESCO World Heritage Committee, composed of 21 UNESCO member states which are elected by the General Assembly. The programme catalogues, names, and conserves sites of outstanding cultural or natural importance to the common heritage of humanity. Ad of July 2015 there were 1031 sites listed.
One of the very few British WHSs of which I haven't had postcards to send people is the Blaenavon iron works. By chance, our cottage was just a few miles from it so we paid a visit to the World Heritage Centre at Blaenavon Library and I bought up their supply of postcards (all 21 of them!)
This is the remains of the water balance tower at the iron works.
And other parts of the same works.