I mean, most caverns don't have much in the ways of features outside of normal cave stuff, unless something resides there. The issue here is that this cave *just* opened up, so it'd be very difficult to justify something living there that needs access to the outside world to prosper. Now if the creature is something that doesn't need sustenance, say an incorporeal creature, such as a shadow or ghost, it makes a lot more sense that it could just *be* there. This is even more true if there is only one way in, one way out, but if there is access to a network of tunnels, you could justify something that has a natural habitat of subterranean, too.

Another question, I saw you post a small map for the frozen area that looked like some form of sentient construction, what was that built for? What was its purpose when it was originally built? This may help to flesh out the dungeon a bit further, or at least give you an idea of what could possibly be within, item wise I mean, because people don't go into a construction project with no purpose behind it, that's for sure.

Like I mentioned before, pick your monsters first, even if it's just room by room, and often times what items that reside there come along with them. Being a cave, if you leave a lot of chambers empty, that is perfectly alright, most of the time they would be mostly empty anyways. I will often times throw little hidden treasures and quirky features into those rooms, just so that they aren't completely empty, and in turn, boring. Doing this will allow a lot of room for DM tweeking, while still doing a bit of room population yourself.

Hope this helps, cheers!

IR