Where is the “XYZ door” in Fez

Tetromino/Tetris block cipher

Controller inputs are only associated with tetrominos once.

Where?

Towards the top of the map, in the tree near the octopus building that houses the solar system model.

What's inside?

A puzzle that displays tetromino blocks based off of controller inputs, and an anticube prize for cracking the nearby pillar's code. (image) (link to finished cipher)

The classroom in the 8-cube Blade Runner city then shows how to interpret the pillars with tetromino inscriptions. Here's one wall, but relate it to the others:

Numbers cipher

Like the alphabet, there isn't one proper way to do this, but you might be interested in the 16-cube temple's classroom. Instead of trekking back, this is what it looks like:

Hint:

Those are "equals" signs, and the last picture is arithmetic. Also, the figure/ground is confusing—pay attention to the box and its internal vertical/horizontal lines, not the "C" shapes. (link to finished cipher)

You have to use the tetromino cipher on the chalkboard.

The answer:

or just press: ↑ ← RT A LT → A ↓, and an anticube will appear