Sh2-155, commonly known as the Cave Nebula, is an emission nebula located approximately 2,400 light-years away in the constellation Cepheus. This celestial object derives its name from the dark, cave-like structure embedded within the glowing gas and dust. The Cave Nebula is a stellar nursery, where young stars are actively forming, illuminating the surrounding clouds of hydrogen gas.

Spanning about 35 light-years across, this nebula is a mixture of bright emission regions, dark absorption areas, and reflection nebulae. The bright portions of the nebula are powered by the radiation of young, hot stars within and near the cloud, which ionize the gas, causing it to glow. Meanwhile, the dark regions represent cooler areas where dust obscures the light from the stars behind them.

The Cave Nebula is part of a much larger star-forming complex that includes several other interesting objects, such as Bok globules, which are dense clouds of gas and dust that may eventually collapse to form new stars.