UNESCO's World Heritage website has an excellent collection and nice, dynamic, map of their World Heritage Properties. A 'World Heritage Property' is a history monument, building, city, or other artificact that meets their criteria of cultural history, creative genius, and importance and gives money and support in protecting the resource.
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.
- World Heritage Convention
Most countries have at least one, and possibly many, some of which are under-utilized. In general, seems like an excellent resource of places to travel and visit. Check out the list by country.
From the world map view, there appears to be quite a high density in Europe (expected) and Central America (unexpected). Central America recieves too little attention as a tourist destination, interesting place to visit in USA culture. As is typical, this is no doubt an effect of modern interests and effects which influences opinion and desires.