Steam's latest hit is a co-op survival game blending Stardew Valley, Terraria, and Valheim

It's hard to summarize everything going on in Core Keeper, but I'd say it's sort of a blend of Stardew Valley, Terraria, and Minecraft, with a bit of Valheim and even some Factorio thrown in for good measure. Plus, it's all set deep underground in the dark… but somehow that doesn't stop it from feeling quite cozy and charming.

And it's already looking like a breakout hit. The indie survival crafting sandbox, which can be played co-op with up to 8 players, launched into Steam Early Access on March 8. Just 48 hours later Core Keeper had already sold 100,000 copies. Now a week later, according to the developer, it's more than doubled that with 250,000 sales.

I can see why. I dove into Core Keeper myself Friday night and kept coming back over the weekend, captivated by the combination of mining, exploring, crafting, cooking, fishing, farming, and fighting.

In Core Keeper you find yourself trapped underground in a massive procedurally generated network of caverns, having been summoned there by the mysterious Core, a powerful yet dormant piece of ancient technology. You start picking away at walls to dig tunnels and collect resources like copper and tin, and use those resources to craft weapons, armor, and tools. Chop tree roots to build a wooden base, collect seeds and create a farm, find underwater ponds for fishing, build bridges to cross deep, dark chasms, and battle powerful boss monsters and their minions. The deeper you dig through the subterranean world, the more you find: new biomes, new enemies, and plenty of secrets and surprises.

After a weekend of play I was feeling pretty satisfied with my progress, having beaten one boss, located another (as in Valheim, you can stumble across boss monster encounters or figure out ways to pinpoint their locations), and worked my way from wooden tools to copper and then tin and finally iron. I've got a nice little farm growing plants I can cook, several smelters for my ore, and even a friendly little NPC vendor living in my house. Yet when I peek at the progress of other players, I can tell I've barely even made a dent in what's hidden deep underground in Core Keeper. Heck, even the trailer above shows a ton of stuff I haven't come close to finding or crafting yet, like automated resource gathering systems and railway networks.

Even though Core Keeper is in Early Access and there are plans to add new biomes, bosses, and more gameplay systems before it's complete, what is already there feels extremely polished and playable. If you're interested, it's also currently 10% off for its launch week, though that discount ends tomorrow.