I have to admit, even though I know "the cave" is supposed to be that dark area just left of center, I'm having a hard time seeing it as that exactly.
There are however a lot of really interesting things going on here like the wispy dark nebulas hanging out in front of the main hydrogen cloud, that big rift of nebulosity streaking off to the upper left, and those bright streamers near the top of 'the cave'.
This is one of the most elusive things I've ever shot and even though the combined exposures of Red/Green/Blue/Hydrogen and Oxygen total 6 hours and 40 minutes, I had to work very hard in the computer afterward to make this look decent.
The Cave Nebula
This is one of those sky objects you can only really see well with a camera, filters, and long exposures. It's one of the few substantial "things" in the sky that doesn't have a listing in the NGC (New General Catalog) or its companion, the IC (Index Catalog) which together cover pretty much anything you would want to see using amateur equipment. But when you start getting pretty 'deep', lurking out there is the Sharpless Catalog of 312 faint Hydrogen regions of the Milky Way assembled by astronomer Stewart Sharpless in two compilations (Sh1 and Sh2) in the mid to late 1950s. We're talking some faint, wispy, dusty stuff here.
Relative positions of the Cave (also known as Caldwell 9) and the Sun
The Cave is 2400 light-years away in the constellation of Cepheus ("The House") which is in the northern part of the sky from Earth, pretty close to the North Star actually. During the Winter we are looking away from the center of the galaxy at night so this thing is just "outside" us in the galaxy and somewhat above us in our little patch of the Milky Way.
This entire nebula fills a volume of space of around 70 light-years so it's not actually all that large, but the fact that it's fairly close makes it appear large in our sky.
The Cave
There's lots of great detail here in the actual "cave" area. Those rockin' bright stars in the upper right are providing the energy to make the gas glow red but there is also a trace of some blue-white reflection nebula action here. I think the translucent dark areas are really interesting with their detail, floating in front of the lit-up hydrogen.
Dark Nebula Details
This is some of the best dark detail in the shot. Some really cloudy looking things in the mid right and those sharp dark wisps in the upper center remind me of "mini Pillars of Creation". You could fit our Sun and all the planets inside one of those pillars.