The initial area remained largely consistent between each iteration.

1971 for Portal 2

Designed to highlight the dramatically acrobatic nature of mobility gels, 1971 is an open test chamber featuring long-distance flings and steep drops. With puzzles centered around the use of repulsion and propulsion gels, building the chamber in an atmospheric old-Aperture science sphere was a given -- as was adding PotatOS to the portal gun. The environment has a single gel source that is used for every portion of the chamber, forcing players to consider how to position themselves in order to keep gaining access to the gels.

Design

Construction on the test chamber began without an overarching plan, and very little planning was done on paper. Instead, simple puzzles were devised on the fly to focus on a specific physical or mental feat. All were developed through trial-and-error as I experimented with various launch and bounce angles to see what might feel fun.

Development of 1971 predates the release of Valve's in-game portal test chamber editor, which now simplifies and streamlines a lot of this process.

In time, a logical sequence of puzzles emerged, and elements were combined and arranged to form the larger sequence. While puzzles build slightly on the ones before it, there's no true learning curve and the chamber is intended for players already familiar with the mechanics. Some elements are immediately obvious to seasoned players familiar with the established conventions of the game: angled white panels, long stretches of barren, paintable surface leading to a white wall, etc.

The new observation room
The redesigned observation room, conveying to players the accidental nature of this portion of the chamber, forcing them to literally think outside the small, elevated box.

The chamber, as ultimately designed, requires a fair deal of exploration and observation by the player. While many Portal 2 chambers have puzzles focused on useable objects -- cubes, buttons, tractor beams, lasers -- and getting them into place, 1971 is more focused on simply navigating the level. To make this more interesting, the number of portal-able panels is greatly reduced, and a portion of the challenge lies in figuring out where to aim and what areas are accessible from the given location.

Redesign

In the underground sections of Portal 2, players generally follow the path through the environment that test subjects would have followed in the past, though they are sometimes forced to deviate due to sealed doors, broken walkways, or other environment gates. In these situations, simply proceeding becomes a puzzle in itself.

1971 was built with this design in mind. Some areas are the original, functional test chamber, which players can proceed through as test subjects once did. Others areas are broken, and proceeding requires subverting the test chamber to get around. After release, an incongruity with this became apparent: The difference between the two was not always clear. A partial redesign was necessary.

The first step was to clarify the original path. Two directional signs were added between puzzles, pointing the way between puzzles that 70’s test subjects would have been intended to follow. The raised room was transformed from an intended area of the original puzzle to an observation room that is now entered out of necessity. For this purpose, the room was given a drastic redesign to bring it in line with Valve’s convention for 1970’s observation rooms. An additional observation room was added to the second part of the chamber.

The new second room
The redesigned second area, featuring a noticable exit door with attention-grabbing indicator lights, and a more precise layout of portal-able panels.

The second room was also expanded and cleaned up. An exit door was added to the far side to provide the player with a clearer goal, and the floor was altered to prevent a liberal coating with gel. Panels were similarly rearranged to better reinforce the idea that the player must get up to speed by using a propulsion gel runaway before entering a portal that is positioned to bounce them across.

For the very last fling, a water-level panel must be used in order to fall far enough to cover the full distance back to a repulsion gel splotch and bounce up to the exit. In order to draw better attention to it, an intermediary puzzle was added. Indicator lights now lead from the closed door to a switch positioned above the panel, but slightly below floor level. Players must now drop down on to the water-level panel in order to safely active the switch as they fall past it. This serves as an introduction to an otherwise-hidden puzzle element that will be used again momentarily.

Similarly, the switch to enable the final fling panel was moved higher and closer to its target in order clearly reveal the result of pressing it.

The Order of Operations

In the end, some 43 different actions -- observational, mental, and physical -- must be taken by the player to complete the test chamber.

The new button
A new button, required to exit the room and forcing players to drop down a path they will later reuse, introduces players to the water-level portal-able panel.
  1. Flinging down into a panel which bounces you back up onto a catwalk
    1. Notice the potential for a propulsive runway
    2. Notice the downward-facing panel atop the tower
    3. Notice the upward-facing panel pointing at the tower
    4. Determine the solution: bouncing down and off the panel
    5. Use the propulsive gel to create a propulsive runway
    6. Use the repulsive gel on an upward-facing panel
    7. Place portals on the runway wall and downward panel
    8. Use the runway to fling yourself into the bounce panel
  2. Flinging blindly across the arena towards no visible target
    1. Notice the blinking light and portal-able wall in the observation room
    2. Use the walls to enter the observation room
    3. Notice the button
    4. Notice the tilting platform when the timed button is pressed
    5. Notice that there is no easy exit from the observation room
    6. Determine the solution: paint the room as a new runway to fling yourself
    7. Use the propulsive gel to create a runway in the observation room
    8. Use the button and runway to fling yourself out of the timed-panel
  3. Flinging up the broken staircase
    1. Notice the broken staircase, preventing normal access up to the next area
    2. Notice the button with a trail of indicator lights
    3. Use the button, which presents a new angled fling-panel
    4. Notice the only accessible portal-able wall
    5. Notice that your portal is still active in the observation room
    6. Determine the solution: use an orange runway to fling up the staircase
    7. Use the portal-able walls to return to either the observation room or main area
    8. Use either propulsive runway to fling up the broken staircase
  4. Flinging across the gap
    1. Notice the gap
    2. Notice the portal-able panel on the floor
    3. Notice the portal-able panel on the wall
    4. Notice the cracked glass, giving access back to the observation room
    5. Determine the solution: use the wall panel and repulsive gel to fling over the gap
    6. Use the portal-able floor panel to paint the floor with repulsive gel
    7. Use the portal-able wall panel to return back to the observation room
    8. Use the observation room as a runway to fling back out onto the gel bounce pad
  5. Dropping past the switch
    1. Notice the indicator lights leading from the closed door to an out-of-reach button
    2. Notice the portal-able panel at the waterline below
    3. Use the panel to drop down, activate the switch as it passes, and fling back
  6. Flinging across
    1. Notice the button
    2. Use the button, illuminating a new portal-able panel on a collapsed tower
    3. Notice the exit
    4. Notice the accessible gels from the high vantage point
    5. Notice the previously-used panel far below
    6. Determine the solution: fling and bounce to the exit
    7. Use the repulsive gel to create a bounce pad on the fling target
    8. Use the water-level panel and the new tower panel to fling and bounce to the exit