Updated June 15th, 2019.
Ever quit Safari by mistake, with a bunch of windows open, then wish you could somehow go back to where you were, with all of those windows open again? If that’s your situation, get back to where you were by starting Safari, going to the History menu, and choosing Reopen All Windows from Last Session.
Every window and tab will magically re-appear. It’s fantastic. Memorize this tip so it’s in your mind when (not “if”) you need it.