Best bang for your buck are UNESCO World Heritage Sites. http://whc.unesco.org/en/list
Roughly speaking, World Heritage Sites are based on either natural beautiful (Grand Canyon and Everglades are in this category), Cultural (Machu Pichu, Angkor) or a combination. According to their website, "To be included on the World Heritage List, sites must be of outstanding universal value and meet at least one out of ten selection criteria.Look up the World Heritage Sites per country."
FYI, Spain has more historical/cultural World Heritage Sites than any other country in Europe. Safe travels!