The book belongs to the genre of hard science fiction. Its heroes are inquisitive inhabitants of the depths of the ocean of Jupiter’s satellite Europa, covered with many kilometers of ice. They are deprived of great physical strength, but have a mind similar to that of a human, enviable tenacity and a funny, but sometimes untranslatable language. Living in darkness, initially diluted only by dim bioluminescence, they develop crafts, technologies, learn the structure of their World, discover neighboring worlds and ultimately cut a window into the Universe. The chronicle of the development of the Europeans covers a period from something similar to our antiquity to a developed technological civilization, developed, but nevertheless experiencing serious crises.