Copy one painting, badly, from a museum bench

Pick one painting — not the famous one with the crowd, the one you'd actually stay in front of — sit on the bench, and copy it in pencil for half an hour. You will be bad at it. That's the point: around minute twenty the painting starts handing over things no amount of standing-and-nodding gets you — a hidden figure, a shadow falling the wrong way, a corner the painter clearly gave up on. Bring your own pencil; the gift shop charges museum prices for theirs.