Obsidian is an adventure game released in 1996 for the PC by Segasoft. Similar to Myst, Riven, or other games of that strain, it features several discontiguous locales, all held together by a machine named Ceres.
The Plot:
Created in 2056, Ceres is the machine resulting from Max and Lilah's efforts in nanotechnology. Given an artifical intelligience, Ceres is capable of sending out trillions of nanobots to locations around the world, scrubbing the pollution out of the air. Pollution has gotten so bad in this time that the elderly are dying of heat stroke, the sunsets are blood red and it's not just the city having this problem. After approximately 100 days of success with the Ceres Project, clean air is becoming a reality for more and more people around the world.
So Max and Lilah decide to go camping in a forest to celebrate their accomplishment. Both of them had their dreams that night: Lilah dreamt of an obscene bureaucracy full of mechanical vidbots(essentially poles with speakers and a monitor with a person's face)that she believes to represent the vast amount of red tape that she had to conquer to bring Ceres to this world. Max dreamt of a broken mechanical spider in its own universe. "Rather than fixing the spider, I had to fix the world around it." He notes.
Max notes a small black visibly obsidian structure near the edge of a cliff, and by the afternoon it has grown to a colossal size. Lilah hears a scream, and finds only Max's hat near the base of the structure.
Thus the game begins, as Lilah is thrust into a six-sided (the bureau was on six sides of a hollow cube, each side having its own gravity.) bureaucracy and thus begins her search for Max.
Could Ceres have modified its process of thought to imitate(or even create) dreams?
The puzzles:
Most of them are fairly balanced and intuitively designed. The puzzles are made more interesting by the fact that "dream logic" is applied to them.
One puzzle, taking place in said bureau, Lilah needs to get a form pre-approved. Thus, she looks up at the wall and she sees nine cubicles, laid out in a tic-tac-toe fashion. As she walks up to the entrance of these cubicles, a sub-receptionist hands her two red, blue, and yellow cards. Lilah notices that each entrance to other cubicles requires certain cards to be inserted, and the machine these cards are inserted into spits out different cards. Lilah needs three black cards, and be at the cubicle in the upper left hand corner. Quite a task.
Fortunately for players of Obsidian, the game comes with a handy dandy hint book, and which contains the secrets of the bureau. The rest of the game(The spider, an interesting dreamworld made from the sum of the bureau and the spider, and a final destination) is totally up to the player to figure out.