Prague's second largest architectural complex after the Castle, this bastion of the Counter-Reformation covers more than 2ha. The Clementinum was built between the mid-17C and mid-18C by the Jesuits. Venture behind its rather austere walls to see its churches, chapels, courtyards and an observatory, as well as a series of splendid Baroque and Rococo interiors, although, sadly, not many of these are open to the public.