There are now two sandbox modes!

The daytime sandbox appears in the bottom-right corner after playing any level. In this level you can use the 5 lowest primes and tools however you like! You can press a button to get a random stone to factor, or a random stone to build. There's also an undo button.

The nighttime sandbox appears in the night shift area, which unlocks after completing level 2 (or going to the last page of the almanac and pressing "access locked levels"). It works like the daytime sandbox, but you have access to all 25 primes under 100! Pressing the random stone button can generate any number from 0 to 101^2!