Photo credit: u/bruckization (Reddit)

Ever completed a puzzle and thought to yourself, “Y’know, this didn’t really challenge me at all”? Kick the difficulty up a notch (or three) with this blank “Krypt” puzzle by Ravensburger, with its 654 unique, solid-color pieces that you must rely on shape alone to properly fit together.

Unlike most puzzles, you’re not assembling a picture, painting, or even a gradient here. The only other clue you’re given is that the pieces form a spiral shape toward the center. If you can complete this thing in under 12 hours, call me impressed.

The puzzle’s available on Amazon in gold ($20) and silver ($14) flavors.