Narbacular Drop

The plot involves the plight of a Princess "No-Knees," so named because she is unable to jump. Captured by a demon, the imprisoned princess discovers that the dungeon she is held in, is actually a sentient elemental creature named Wally. Using Wally's portal making ability, the princess sets out to escape and defeat the demon.

While Narbacular Drop features a 3D world reminiscent of such first-person shooters as Quake, the unique portal element and the character's lack of a jump ability makes navigation and puzzle-solving very unconventional. The player can open a single pair of interconnected portals at a time, each styled as a huge face with flaming eyes (red or blue to tell them apart as the player repositions one or the other) and an open mouth big enough to see and walk through. Positioned with a point-and-click interface controlled by the mouse, portals are allowed only on natural surfaces and are prohibited from any metal, lava or other artificial surfaces in the game. Aside from the portals, important game elements include switches, boxes and huge rolling boulders which can crush the character. The player cannot save game progress.

Source: Wikipedia, "Narbacular Drop", available under the CC-BY-SA License.