Nebulas were common environments in the universe, and there were differences in size. The smaller ones might only be the size of an ordinary star system, while the larger ones could encompass hundreds or thousands of star systems.
Due to the concentration of interstellar space matter in the nebula being too large compared to the vacuum universe, it could block the transmission of various waves. Ordinary detection methods would not work in such a place.
For some early interstellar civilizations, the nebula was a natural secret base. As the detection waves outside could not reach the depths of the nebula, these interstellar civilizations could hide many important facilities inside. They could even transform the planets in these places into secret bases in hopes of catching them off guard one day.
