My partner and I climbed the Hill to the Vitkov National Monument on a Monday having spent our entire weekend in the Old Town and Jewish quarter. The area is a bit odd and we weren't sure if we were in the right place until we got there. It's away from the main tourist area and poorly signposted.
So we finally arrived to find it is closed on Mondays so this review doesn't cover what is inside! However I would still recommend going on Monday. The monument is huge and very photogenic when there are no crowds. It makes for a very serene and reflective moment to sit on the steps and gaze over the Prague skyline with only your thoughts for company. Highly recommended if you've spent the weekend surrounded by crowds and traffic.