Cyan Worlds

More than 10000 years ago in the caves of southern North America found its refuge Empire Days of civilization. The people possessed supernatural Days craft - Art inscription. With this trade, they created a Books of the displacement. These manuscripts allowed people to move between worlds, which they called "The Age".
People Days flourished for thousands of years, but once there was an accident completely destroyed their world. Their subterranean dwelling was completely devastated, and all the books, and Epoch respectively, were lost before our time.

Riven's two major puzzles require solving several miniproblems that in turn require close observation of Riven's denizens, colors, and unique numbering system. Gathering those elements becomes routine but just as you get comfortable with the concept there is a clever extra challenge tossed in - a missing color, a broken device, an obtusely revealed animal. Much of Riven's prerelease PR emphasized the environment as a source of clues and puzzle solutions. It is, but not to the large extent and subtle degree you may expect.