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Portal is not a particularly challenging game control-wise. It is, however more challenging mentally than others, albeit only in the later levels. Completing Portal requires a mind which fully understands how portals work and can apply the physics behind them to any situation. It also requires good control skills (for those awkward jumps), and only rarely does it require good timing.

The game is split up into twenty different test chambers, with the difficulty rising in a logarithmic fashion. After chamber 19 (actually the 20th chamber, since numbering starts at 0) is complete, there are three escape levels where you escape the Aperture Science laboratories. Once the game has been finished, you can play the advanced and challenge chambers. There are six advanced chambers, which are ordinary levels with extra obstacles and challenges added to make them that little bit more impossible. They are unlocked as you complete each corresponding normal chamber. The challenge chambers are chambers 13-18 with extra challenges added, and the aim of completing them either…

• using as few portals as possible,
• as fast as possible or
• with the fewest number of footsteps possible.