Challenge

Complete the timed Challenge in the Caves. Turn on the record player at the back to start, then solve the procedurally-generated puzzle gauntlet before the roughly six and a half minutes of music (Grieg's "Anitra's Dance", then "In the Hall of the Mountain King") runs out. There's no fixed solution - it demands fast on-the-fly solving - and it's one of the hardest achievements (about 3-4%).