Terraria was, once upon a time, a game about digging down: you started as a surface-dwelling weakling and mined your way to the planet's molten core, hauling the resources back up to build cooler and more elaborate tools and structures. That's still in Terraria, though after a decade of updates it's so much more, with quests and elaborate boss fights and expansive building tools and unique "world seeds" that change how the world is randomly generated. Today's Labor of Love update makes a huge number of additions, but the coolest may well be the Don't Dig Up world seed, which flips the game topsy turvy.
Here's the description straight from the patch notes:
"An idea first discussed during the release of Journey's End, Don't Dig Up turns the world of Terraria upside down—literally! The player will begin their adventure in the depths of the underworld, complete with all new flora to help provide early resources.
"As the player ascends into 'The Up', however, the threats will magnify exponentially until they reach the Surface—a truly horrifying and inhospitable place that will test the mettle of even the most seasoned Terrarian. Rethink everything you know, but Don't Dig Up unless you are prepared for what comes next!
The name is literal here. The surface now looks like hell, with a lava-filled backdrop just like the depths of Terraria would normally have. The enemies aren't late-game monsters, though: they're just nice little slimes. Nice little flaming slimes. You can only dig a short way down before you hit bedrock, which means the only way to progress is to go up. And the patch notes sure don't make it sound friendly up there.
Creating an upside-down world is easy: just start a new world and type "Don't Dig Up" in as the seed. You'll know it worked pretty quickly.