Narbacular Drop is an environmental puzzle video game developed by Nuclear Monkey Software. It was released for free online in 2005 for Microsoft Windows. It was the senior game project of students attending DigiPen Institute of Technology. The gameplay consists of navigating a dungeon using an innovative portal system. The player controls two interconnected portals that can be placed on any non-metallic surface (wall, ceiling, or floor). Gabe Newell, managing director of Valve, took interest in the team's work and employed the whole staff at Valve. The developers went on to write the critically acclaimed Portal using many of the same concepts.

The word 'Narbacular', which does not exist in any dictionary, was chosen primarily to aid in internet search engine results.

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.

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