On a budget, weigh it — Dancing House isn't cheap for what it is.
Free (exterior); rooftop bar minimum spend
A genuinely clever bit of deconstructivist architecture and a refreshing modern note in a baroque city; the rooftop terrace gives a nice river-and-castle view. The catch: it's an office block, so apart from the rooftop bar/gallery there's nothing to enter, and from street level it's a two-minute photo. Worth folding into a riverside walk, not a special trip.