Sh2-155 is a diffuse nebula in the constellation Cepheus, within a larger nebula complex containing emission, reflection, and dark nebulosity. It is widely known as the Cave Nebula.
The Cave Nebula is an ionized H II region with ongoing star formation activity, at an estimated distance of 2400 light-years from Earth.

Technical info: 
TS 80mm f6 APO triplet refractor
Canon 40D (astro-modded) - IDAS Light Pollution Filter LP2
Canon 40D mono + 12nm Ha filter.

Exposure: Mono - 72x 10min - (taken over 3 evenings).= 12 hours
Exposure RGB - 129x 6 min = 13 hours
Total exposure - ~25 hours