The Invincible is a gripping science fiction novel by the renowned Polish writer Stanisław Lem, first published in 1964. It follows the journey of an interstellar 2nd-class cruiser, aptly named Invincible, as it lands on the bleakly uninhabited planet of Regis III. The mission: to investigate the mysterious loss of its sister ship, Condor.

Maintaining the highest security measures, the crew embarks on a daring search for the lost Condor. Meanwhile, the scientists among them delve into researching the enigmatic planet, striving to identify any lurking dangers. As they explore, they stumble upon unknown structures, reminiscent of an Earth city, and eventually find the Condor some three hundred kilometers away (roughly 186 miles).

As the story unfolds, the crew encounters beings that have seemingly evolved from autonomous, self-replicating machines, possibly the remnants of a "robot war." Navigating this strange new world, they are forced to confront the classic quandary: what actions should humanity take when faced with the limits of its knowledge?

Lem masterfully blends elements of mystery and adventure, challenging his characters—and readers—to confront the inexplicable and the bizarre, pushing the boundaries of human understanding.