The holidays are different in each country, and in many countries, there also are
local and regional holidays.
This is the web-based holiday finder that I use, but there are many others.
The point is to consult one or run the risk of being surprised by closings:
We have found that in places like Paris and Rome, there often are unscheduled closings.
It pays to call ahead, even the day before. When they give reasons, they point to work stoppages, employee absences
or budget cuts. I heard a sad story about a valuable day in Paris being lost to on a daytrip by bus and rail to a palace
outside the city that was closed. All I can say is, try to be philosphical and roll with the punches, but call ahead
if at all possible.