The greenest park in Croatia. Its main feature are the two lakes, both warmer than the sea, and also the local flora and fauna.
Wikipedia (Croatian) http://hr.wikipedia.org/wiki/Nacionalni_park_Mljet
More information about the island http://www.mljettravel.com/national-park.html
Address 20226, Croatia
Coordinates 42°46'36.462" N 17°22'56.884" E