Portal was released on October 9, 2007 by Valve.  Portal was also developed by Valve. This game is a puzzle presented from the first person perspective.

Everything that you’ve heard about Portal is true; well almost. The use of portals is hardly new, Prey used them long before this game surfaced. Portal is an entirely different kind of game.

Players must solve physical puzzles and challenges by opening portals to maneuvering objects, and themselves, through space. In Portal, the player controls the protagonist, Chell, from a first-person perspective as she is challenged to navigate through a series of rooms using the Aperture Science Handheld Portal Device, or portal gun. A game where you are a lab rat for a crazy artificial intelligence who makes you do experiments in exchange for a vague promise of cake.

The portal gun can create two distinct portal ends, orange and blue. The player can go back if desired the portals are not unidirectional. As the player pass through a blue entrance, the other side is orange. This is akin to a dog chasing its tail as the portals tend to not be very easily oriented to the desired location.

As moving objects pass through portals, they come through the exit portal at the same direction that the exit portal is facing and with the same speed with which they passed through the entrance portal. This game is déja vu in spades.

Although Chell is equipped with mechanized heel springs to prevent damage from falling, she can be killed by various other hazards in the test chambers, such as turret guns, bouncing balls of energy, and toxic liquid. She can also be killed by objects falling through portals, and by a series of crushers that appear in certain levels. Unlike most action games at the time, there is no health indicator; Chell dies if she is dealt a certain amount of damage in a short time period, but returns to full health fairly quickly. Some obstacles, such as the energy balls and crushing pistons, deal fatal damage with a single blow.

Chell and all other objects in the game that can fit into the portal ends will pass through the portal. However, a portal shot cannot pass through an open portal; it will simply deactivate or create a new portal in an offset position. Creating a portal end instantly deactivates an existing portal end of the same color.

Moving objects, glass, special wall surfaces, liquids, or areas that are too small will not be able to anchor portals. Chell is sometimes provided with cubes that she can pick up and use to climb on or to hold down large buttons that open doors or activate mechanisms. Particle fields known as emancipation grills, occasionally called “fizzlers” in the developer commentary, exist at the end of all and within some test chambers; when passed through, they will deactivate any active portals and disintegrate any object carried through. The fields also block attempts to fire portals through them.

There are many ways to solve a given puzzle so the game has some replay value to it. Skilled players will portal their way through the nineteen levels in just a few hours.