(No, I haven't just gone and jeopardized Mithrandir's entire series, I have been given permission by him to do clue 21.)
A note from @Mithrandir: I have given explicit permission for @BeastlyGerbil to post this, and gave him the answer to encode. If you want to post one, ping @Mithrandir in chat and we'll talk.
Before you can even have a moment to celebrate solving the previous clue, a trapdoor opens beneath you and you fall into darkness. You scream before opening your eyes to find you are no longer falling but landed on a padded floor. The trapdoor is just above your head but just out of reach.
You look around and are confronted by a picture which on first appearance seems to be levitating in front of you, though you suspect there are wires, suspending it from the ceiling, hidden in the darkness. You move forward to scrutinize the picture more.