6. Co-op Vents
It's pretty easy to complete, but there's a lot to like about Co-op Vents. You and your partner split off into two separate corridors (or vents, I guess), which intersect at rooms designed to put one player's life in the hands of the other. The difficulty lies less in the puzzles themselves and more in resisting the urge to blow up your friend. Download Co-op Vents here .
Notes from the Testing Partner: "What is it about lasers that turns you into a homicidal maniac?."
Rampage heavily explores the possibilities of hard light bridge based puzzling. The three rooms use a mixture of ramps, bridges and emancipation grids to create interesting and unique challenges that require some seriously involved portal co-ordination. Also smart: It allows respawned players to easily make their way back to where they died. It's a problem in some maps, thanks to a level editor that doesn't allow checkpoint placement. Download Rampage here .
Notes from the Testing Partner: "Wait, STOP! Not yet! *splash* DAMN IT!"
8. Quest for the Edgeless Safety Cubes
In which you must find three spheres to unlock the exit, each hiding behind some difficult puzzles in sub-chambers that themselves can be hard to access. The main puzzle room is full of buttons and laser-activated switches, and just deciphering what controls what is a challenge. Despite that, the level has some well crafted puzzles that require inventive portal work to complete. Download Quest for the Edgeless Safety Cubes here .
Notes from the Testing Partner: "I meant to die there. It was tactical."
Mazed casts you as lab rats, working through corridors looking out onto a large, unreachable cube. Each player must help the other to progress through their respective routes. What at first starts out as simple switch activation soon becomes an involved series of timing challenges and backtracking in order to make a small bit of progress. It's a strangely claustrophobic experience. Download Mazed here .
Notes from the Testing Partner: "I should have picked your route. There's less pissing about with turrets."
10. Super Happy Fun Time
Finally, a one room puzzle that features lots of thinking through the use of an excursion funnel as it pushes and pulls cubes and players through four portals and a variety of improbable obstacles. The division of labour is a bit off balance, with one player required to do little more than push buttons at the right time, but the central problem requires plenty of discussion to overcome. Download Super Happy Fun Time here .
Notes from the Testing Partner: "Sure, the bit with the funnel was fun. But super happy fun?"
Bonus: Geolocity Stage 2
As with the single player maps, some creators prefer to use Hammer, the Source engine's level editor, to create more detailed works. Hammer's co-op selection is less focused on custom campaigns than the solo stuff, but its use still enables handy additions like visual variation and player checkpointing.
It can also be used to reimagine Portal 2 as something else entirely. Something like a racing game. Geolocity Stage 2 abandons puzzles for a track covered in orange speed goo. You have to run, jump and portal your way through the course, avoiding plenty of obstacles and thinking on-the-fly to get through some tricky sections as quickly as possible. While the first Geolocity is also a lot of fun, Stage 2 adds in the ability to screw over your opponent with targets that, when activated by the ping tool, can reverse excursion funnels, create barriers or activate crushers. Download Geolocity Stage 2 here .