https://www.pcgamer.com/destiny-2-is-free-to-play-this-weekend/

The weekend is upon us, and if your schedule is still open and you're looking for a game to play—and you haven't yet immersed yourself into the endless gunslinging joy that is Destiny 2—then you'll be happy to hear that it is free to play for the weekend. 

To do your bit as a nigh-immortal Guardian, point yourself at Battle.net and download the installer. It's a 4.5MB download, but of course the full game is a lot bigger than that—It'll eat up around 63GB of drive space once all is said and done. But once it's all set up, you can play as much as you want across all modes and through the entire campaign. (And really, a good weekend should be quite enough to finish the campaign, but the good stuff doesn't really start until it's over.)