See that big sale off in the distance? You can actually walk there. That's pretty boring though, so thankfully there's a fast travel system. All you need to do is hit this link and be instantly transported to Steam's new open world game sale.
Or you can accept this side quest, and hop into the post for some of my personal picks.
Steam considers "open world" a theme rather than a genre, and so the games on sale run the gamut from first-person action, to driving games, to strategy games, to survival games. Is survival management sim Oxygen Not Included really open world? Is Teardown, because although its levels are small, you can smash through the walls in any direction? Who cares - they're good games and they're cheaper than thety were before.
I recommend free-roaming RPG Kenshi, which is 40% off and £13.79/$18/€16.19. It's brutal, but is one of the best RPGs and best survival games. I recommend Death Stranding, again, which is reduced 50% to £27.49/$30/€30 and will send you on an Icelandic road trip with an encouraging jar baby.
Finally, I recommend turn-based tactics RPG Battle Brothers, which is also reduced 50%, to £11.49/$15/€14. It's about leading a small mercenary company and trying to survive an open world campaign filled with bastards.
You can obv have a poke around yourself, and make your own recommendations in the comments below.