Portal fans will have learnt from the first foray through Aperture Laboratories that, when it comes to running a gauntlet under the watchful eye of GLaDOS, things aren't always what they seem.
Thankfully, Portal 2 shouldn't disappoint conspiracy theorists and Easter Egg hunters. Valve's packed it with more than enough hidden references, secret side-glances and mysterious nods to Portal's untold past and some small-time franchise called Half-Life.
But how can you feel the satisfying swell a freshly discovered secret brings if you can't find the darn thing in the first place? With our help, that's how.
Here are the Portal 2 secrets you might have missed:
Final chamber, Chapter 7
There's a portrait in a hidden room after the ﬁnal chamber of the seventh chapter. It's of Cave Johnson and 'Caroline' - Cave's trusted assistant until his death in (we suspect) the 1980s - in a very Mastermind-like pose (stick 'Mastermind game' into Google images, sweet youth).
On Caroline's death, Cave transferred her consciousness to the Aperture network, thinking only she was capable of running the company. Find the painting and GLaDOS mentions 'knowing those people,' presumably because she holds Caroline's existence within her memory banks. You'll also be rewarded with the 'Portrait Of A Lady' Trophy.
Final chamber, Chapter 6
At the end of Chapter 6, ﬁnd the ofﬁce with a sliding door in the corner. Beyond is a litter of life belts marked Borealis - the Arctic ship referenced in Half-Life 2: Ep 2 and suspected as the focus of Ep 3. You're standing in the dry dock it was launched from. Cave tells you about a teleportation experiment where the ship was lost...
Chapter 3, Room 16
There's a turret behind a grate in room 16, chapter 3. Use the laser in the nearby room to fry the grate. Scoot through and you're treated to an impromptu singing performance, led in choir by a jolly-looking fat turret referred to as the 'soprano'. You're safe: the little things are enjoying themselves too much to look up and shoot you. Consider it a warm up for what's to come when you ﬁnish the game.
Beginning of Chapter 5
Early in Chapter 5, ﬁnd the parts-covered conveyor leading to an incinerator and listen for the turret yelping, "I'm different!" Pick it up and it directly references some Cave Johnson sayings - discussing lemonade and 'getting mad' - as well as Caroline and the myth of Prometheus. Hmm, prescient... Sadly, you can't leave the area with the turret. It may be different, but it won't be free.
BREAK THE RULES
Chapter 2, Chamber 7
Every chamber ends in an emancipation grille: a fuzzy blue ﬁeld that dissolves anything GLaDOS decides you shouldn't bring with you. Every chamber bar one. The grille in the seventh room of chapter two is on the fritz, meaning the careful among you can extract the weighted companion cube - denoted by the heart - from the chamber. Whereupon, with GLaDOS being GLaDOS, it's dissolved in front of your eyes.
Scholarly fans claim the plot is a Greek myth. Prometheus and Epimetheus created humanity, but Epimetheus (Wheatley) was useless. To help, Prometheus gave humans ﬁ re (GLaDOS gave Chell the Portal gun) and was cast into the pit of Tartaros for it. Signs? Elysium was a heavenly ﬁeld of reeds, and P2 ends in a ﬁeld. The depths of Aperture have 'Tartaros 9' on the walls. And the painting of Caroline and Cave shows Aeschylus - writer of Prometheus Bound.