Very Complicated Chemistry related question

Ok, lets say i had a Cube Rite, its inside was 3x3x3 Meters... (27m^3). And for a hypothetical it had a border 1 meter thick of super strong material surrounding it, to make sure it could not break or be altered in any way possible.

Then i filled the whole inside of the cube with water, the whole 27 cubic meters...

Then I froze the water.

Since water expands when it is frozen and the cube cannot change shape (unalterable, superstrong material) what would happen to the water?

If you just lower it to like -3C then it would still be liquid, but it can form amorphous ice at VERY high pressures.