Closure Days in Italy
Buongiorno,
It is true that museums and monuments are normally closed on Sundays - however always be sure to check the schedule because sometimes they also have special hours and opening times.
This rule does not apply to restaurants. Every restaurant normally has a day that it is closed and this will be indicated on the sign that gives you the opening houses.
Some stores - like food stores and newspaper stands will open on Monday with normal hours but there are stores that have a late opening time on Monday - if this is the case they will usually open after lunch.
Buon Viaggio