The Witcher: Enhanced Edition Director's Cut is free forever via GOG Galaxy.
To get CD Projekt's fantasy role-playing game, you have to download the GOG Galaxy app, go to "recent" view and click to claim The Witcher. Then the game should show up in your games library inside the app and in your GOG.com collection.
CD Projekt's 2007 The Witcher has been made free to download a number of times over the years, but it's worth flagging this promo as it comes just a handful of days before the launch of Cyberpunk 2077. So if you fancy getting stuck into a big old RPG in the week before CD Projekt's next big old RPG comes out, here you go.