Episode 20 of The Witness opens in a dark room under red windows, at a row of three gray panels with the blue subtracting symbols seen in Episode 18. Basket solves the row, walks out onto the red side of the marsh, sends a beam of light toward the mountain, and spends the second half of the video on a boat tour of the island.
Three gray panels
The first panel in the row is already solved when the video starts. "Almost whatever you do is okay," the commentary says early on, but the second panel still takes about five minutes of lines before one goes blue.
The third holds more shapes and more of the blue symbols, and it fights back. "You can't have more negation than objects, so that's not gonna work." The commentary asks for a vague hint if anyone has worked it out, and a moment later: "Oh, that was dumb. There we go. I figured it out. Okay. I had to group them." The line turns blue and a blue cable lights up along the wall.
The red side
A doorway opens onto walkways over red water, in tall yellow grass, with metal cages along the paths. "It's the red side! The red side's the side I couldn't get to."
Small red panels stand on posts here. Solving them changes the walkways around them: "depending on which things you section off, it drops down the floor." Another raises a wall. The commentary notices "there's one on this side too," uses it, and climbs up: "Amazing. I'm so cool."
One more beam
At the top sits a yellow box with a device on a pole. "One last laser beam to the sky, guys!" It turns and points up and away. The commentary reads it as the end of an area, a beam aimed at the mountain, and guesses "there's probably four more laser guns around that we still need to do."
Getting back out takes the cage panels again ("they make it complicated"), then a shortcut and a rocky path down to a dock.
Around the island
Basket takes the boat. On the way, a recorded voice reads a passage about an empty boat drifting into another: nobody gets angry at an empty boat, only at one with someone in it. The commentary calls it "an interesting point" and says it "makes you think on this long boat ride." A speed control turns up the pace: "Yes, I can go faster."
The ride passes old ground. The commentary points out the tree fort whose beam it could not quite get, a town with puzzles left unsolved, a ship with "a very confusing puzzle" inside, and a building with no error marks at all: "Whenever there's no error indicators, I just can't figure it out."
Where it ends
"So we haven't been in that castle, so maybe that might be a cool castle to go to." The boat pulls in at a stone pier below a building with a tower, and the video ends there, before Basket steps off.