This article covers Graz and Linz. Each of them can be visited on a day trip from Vienna, and each can sustain a longer stay for those inclined to more in-depth exploration.
The central area of Graz is recognized on the UNESCO World Heritage list as a wonderful architectural ensemble – and it is true, architecture delights await you at every corner.
The historic center converges on the dazzling Hauptplatz ♥♥♥ which is dominated by the imposing Town Hall. The comparatively wide Herengasse ♥ houses a number of fascinating buildings. The narrower winding and climbing Sporgasse ♥ is another headline street.
Cathedral ♥♥ is well worth exploring. The neighboring St Catherine’s Church appears more colorful on the outside and holds the Mausoleum with tombs of some of the Hapsburgs.
Uhrturm ♥, at the edge of the public park at Schlossberg ♥, stands guard over the town. Its clock hands are the opposite of what we expect them to be (the smaller shows minutes, the bigger hours), which adds to its quirkiness. You can take panoramic views over the city from under the tower. A stairway descending to Schlossbergplatz from the hill offers additional opportunities for elevated perspectives, with benches at many of its landings. If you have time to linger, consider catching the sunset here (a recommendation I read elsewhere but had no ability to test).
Schloss Eggenberg ♥ is away from the city center, reached by tram and then some walking. Its interiors are open to visitors only in summer, but you can walk into its courtyard, go up the galleries, and also explore the gardens year-round (you can also peek through the glass doors for a glimpse of a ballroom when the castle is otherwise closed). Peacocks in the garden provide additional entertainment – there are at least two dozen of them.
Other attractions that are likely worth checking out when in Graz include: Kunsthaus, Landeszeughaus, or Basilika Mariatrost (the latter is located some distance from the center).
If you travel to Graz by train, a portion of the trip will be over Alpine terrain via the Historic Semmering Railway, a UNESCO World Heritage site, on the stretch of 41 km between the towns of Gloggnitz and Mürzzuschlag. Look out the windows for glimpses of its remarkable viaducts; in all fairness, the railway is best explored by driving along, which would allow you to stop at strategic viewpoints to take pictures of said viaducts.
Not as pretty as Graz overall, Linz nonetheless has a number of points of interest and plenty of colorful houses in the historic center.
Hauptplatz ♥ is large and surrounded by interesting architecture. From here, streets in different directions offer pleasant walking routes through the historic core. One path takes you over the Danube to a quieter part of town. Walk over the bridge ♥ for great views of the river and the town on both banks.
Mariendom ♥♥ is a grand church with stained-glass windows among its most impressive features. Old Cathedral is potentially worth a visit if accessible.
Postlingberg ♥ is an elevated point with Postlingbergkirche ♥ worth checking out, but the area must be more interesting in the summer. The tram line ♥ connecting it with the city center should be used at least in one direction, and probably both.
Among considerations for a future visit are: Linz Castle, Schlossmuseum, Ars Electronica Center.