Theatre at Epidauros
The theatre at Epidauros is not just one of the earliest existing examples of human theatre, it's also a magnificent example of integration of landscape and architecture -- so well done the architecture almost seems to 'complete' the pre-existing landscape.
This is an often overlooked feature of early Greek architecture. Describing the theatre in their book The Landscape of Man, Susan and Geoffrey Jellicoe suggest that this "genius loci, the recognition and expression of the spirit of particular places, has been the most enduring legacy of Greece in landscape design."
Architecture stood for universal order. The existing landscape was without apparent order, and the Greeks not only harmonized two seeming opposites, but gave to the whole a significance which civilization is only now beginning to accept is not pertaining to Greece alone...
The theatre at Epidauros (350BC) is protectively modelled out of a north-west slope. The sun is upon the players, and the theatre is an almost perfect instrument of sight, sound, player-audience association and landscape affiliation -- the climax in form of the Greek philosophy of the unity of all things.