Portugal: Castelo Dos Mouros in Sintra
Castelo dos Mouros or Castle of the Moors is a medieval citadel built in 8-9th centuries during the period of Muslim Iberia. The fortress sits on top of Sintra Mountain which makes it impregnable to begin with. On top of this there are several layers of walls and round defensive towers. Spectacular views from pretty much any point in the fortress. Its a UNESCO World Heritage Site.