Your thinking of Space
Hulks, which are usually mashups of many old ships, space stations, other ruins and wreckage, asteroids, and whatever else gets mixed in over time. They jump in and out of the warp at random or on semi-predicable routes.
Sometimes the wrecks of extremely large ships can become space hulks all by themselves. (see Judgement of Carrion for an example of such a Space Hulk in the Dawn Of War video game series)
space hulks can be infested with nids, cultists, orkz, and all kinds of other stuff.