The baroque library hall and the climb up the Astronomical Tower for a 360° Old Town view are a quieter, more curated experience than the castle crowds. The honest catch: it's guided-tour-only on fixed slots, the tour is fairly brisk and you can't linger or photograph freely in the hall. Book ahead in season or you'll be turned away.
Founded by the Jesuits in 1556; the Baroque Library Hall was built 1722 by Kilián Ignác Dientzenhofer with frescoes by Jan Hiebel. · en.wikipedia.org
The Astronomical Tower's viewing gallery is reached by 172 steps; library hall and tower are seen on a timed guided tour only (you cannot enter the hall). · prague.eu