If you played through the whole game and want to do something offline, here are some nifty suggestions.
The easiest and very hands-on is this paper craft: your own hexahedron paper cube!
Source: ProtectionKooky1517 on Reddit.
Still in the cube spirit, some people are very good at modeling stuff for 3D printing. You can create your own, or maybe buy the cube, or the model?
Source: TheDonutBoy on Etsy.
Some other creative people decided to make real life versions of the writing and counting cubes.
Source: randy_s on Printables.
If you enjoy aquabeads, or any similar type of beads that can be put on a grid, you can try creating Gomez or any other character or item from the game.
Source: KiNoKoSHOP on Etsy.
Ok, that's maybe just slightly offline, but still on a computer. There are several tutorials and communities dedicated to modifying the game, using the original assets to create new worlds or levels. I'd recommend starting with the Fez Modding website or their Github, but there is also another tool on Game Banana.
Source: Fez Modding on Github.io.
With similar resources, you can create your own little FEZ's world, for image purposes only. I think the website "Sprite Resources" is a great start, but you can also learn how to extract the assets on your own.
Source: Fez on Sprite Resources.