The Strahov Monastery complex.
Founded in 1140 the monastery looks down from Petrin Hill over the area of Mala Strana. It was destroyed by fire in 1258, but rebuilt in gothic style and had baroque additions later.
Over 800 years old, and despite being ransacked by invading armies, it is still a working monastery. It it has a famous library with one of the oldest collections in the country, holding over 16,000 books.