Cave Nebula (Sh 2-155)
Sharpless 155 (Sh2-155, LBN 529) is a bright H-II region of a major nebula complex (Cepheus B molecular cloud) consisting of emission nebulae, reflection nebulae and dark nebulae, stretching over the constellation Cepheus. The nebula, about 2400 light-years away, is an active star-forming region. Young stars of the OB3 asterism are responsible for the ionization of the gas. Radiation from the hot O-type star HD 217086 is thought to be compressing gas in the region, triggering new star formation.
In the animated fig. 3 one can see how in the infrared (section WISE, Wide-field Infrared Survey Explorer) the dust clouds emerge brightly, which appear dark in visible light (section DSS, STSci Digitized Sky Survey).
The name "Cave Nebula" probably goes back to the English amateur astronomer and book author Sir Patrick Moore and his Caldwell catalogue, which was published in Sky & Telescope in 1995. Sh2-155 is listed s Caldwell 9 there.  The arch in the nebula looks like the entrance of a cave. The name «Cave Nebula» is also used for the reflection nebula Ced 201 and VdB 152.
Further infos at CDS: Sh2-155
RA : 22h 57m 05.9s Dec : +62° 38' 09" Mag : 7.7 mag Grösse: 50' x 30'
Sh2-155 is located in the eastern part of the Cepheus constellation. It is circumpolar for Central Europe. The best observation time is May to December.