Saturday is easy. Sunday is where you find out which ideas really hold. More things are closed, hours change and without a car, "let’s do something spontaneous" can turn into dead time very quickly.
The best Sunday rule is simple: one destination, one backup, one clear way home.
Short version
On Sundays in Salzburg City, places with clear opening hours, simple routes and little friction win almost every time.
If you want to get out
1. Gaisberg
One of the few real outing options that still feels like getting out without needing a car.
2. Salzach or Altstadt loop
If the budget is tight or you only want two hours, one clear walk is often better than a half-hearted indoor plan.
If you need one clear indoor anchor
3. Hangar-7
A very good free Sunday anchor.
4. Haus der Natur
Useful for mixed groups where not everyone has the same energy.
5. The library or another calm city place
On some Sundays, you do not need "program". You need one clear low-pressure place.
What is different on Sundays
6. Small groups beat big groups
Two to four people usually work much better.
7. The way home decides
Especially on Sundays, the return trip should be part of the plan from the start.
8. Less is often more
One solid destination plus one short second step is usually enough.
9. Bad weather needs an early Plan B
Sunday plus rain is exactly the combination where groups collapse fastest.
10. Repeatable Sundays are gold
The best ideas are not the most spectacular ones, but the ones you could use again in three weeks.
Conclusion
Sunday in Salzburg without a car does not have to be dead. But it needs more honesty than Saturday. Good Sunday plans are clear, reachable and low-stress.