I'm planning a few days in Venice in early Oct 2017. Will any major attractions be closed, such as St. Mark's? This will be second visit to Venice. Thanks!
Wherever we travel, I make a list of the sites I want to visit and then painstakingly go to their websites and search for days and hours open, as well as planned shutdowns for remodeling, etc. I know of no better way to do it. If I do the research myself, I can (usually) depend on it. Sometimes a guidebook will cover planned closures but you have to have the latest version and even then the data is sometimes out-of-date by the time it is printed.
If I have specific questions regarding a destination, I have found that contacting the official tourism organization for the city or country is usually helpful. In this case, you might contact:
http://en.turismovenezia.it/