In order to open the archives, you'll need to enter the password. See password.txt for that information.
You'll also need 7zip. Download 7zip here: https://7-zip.org/

I've also received at least one report that the universe.7z file triggers Windows Defender. It claims there's a Trojan inside. I have no clue how that's possible because the archive is literally just .world files. There's nothing else inside, no exes, the entire content of the 7z is exactly the same as what you see in downloads/universe, just compressed.

So to help put anyone at ease, here's the Virus Total scan results for the file.

https://www.virustotal.com/gui/url/bbd75276310e904847490fe8d99b7d91a9e44c054e3d3b7e2abb28b9e63d7e7c/detection

Note: My Windows Defender doesn't react to it, so if yours does, I guess try running Windows Update? Maybe an older version of Defender gets confused.