Vienna's imperial past is concentrated enough to see the essentials in a day or two if you prioritize well. Schönbrunn Palace and its expansive Schönbrunn Gardens reveal the Habsburgs at their most ambitious, while the Hofburg Imperial Palace shows where that same dynasty actually ruled from for centuries. St. Stephen's Cathedral anchors the Innere Stadt, the compact old town where most sights sit within easy walking distance of each other. Add the Kunsthistorisches Museum for one of Europe's great art collections, and the Belvedere Palace for Klimt and baroque grandeur, and you have a shortlist that captures Vienna's architecture, art, and history without wasted time crossing the city.