All weekend long, publisher Paradox Interactive is hosting a huge sale on Steam in conjunction with its PDXCon Remixed digital convention. The Steam Paradox Interactive Sale, which runs until May 24, includes discounts on PC games like Crusader Kings III and Empire of Sin. On top of all the game deals, three titles are free to play for the next few days: Cities: Skylines, Stellaris, and Surviving Mars.

Both Cities: Skylines and Stellaris serve as pillars in the 4X genre, helping players get acclimated to the genre's rather slow output. Not quite a 4X game, Surviving Mars features many of the same city buildings elements players can expect from other Paradox-published strategy RPGs. All three games can be downloaded and played with no strings attached until May 24. If you end up enjoying them and want to keep playing, you can buy either of these Paradox-published titles at up to 80% off

The sale also slashes prices for other titles from the publisher's catalog. This includes strategy RPGs Crusader Kings III at 20% off, Empire of Sin at 50% off, and Surviving the Aftermath at 25% off.