So, you've finally defeated Flying Dragon Agheel, explored a little bit and then found a chest that teleported you somewhere. Excited to explore a new area, you go out and fight the first foe you come across, only to find out that your weapon clinks off of their armour, and you might as well be fighting them with a feather. Any attempt at teleporting out is futile as well since you're locked out of doing so. It also doesn't help that if you run down the wrong path, you come across easily one of the hardest bosses in the game — the Fallingstar Beast.
At this point, I was befuddled on where to go, what to do, and how to do it. Well, fear not! For I found my way out after running around aimlessly, and I've made a video sure to guide you straight out of that hellhole.
You might die in the process of escaping because of a guard NPC that shoots some spikes in your direction; in the video, I fail to avoid the spikes, but with enough rolls, you should be able to save yourself any damage.
You'll want to run out of the shack and hug the right wall until you are behind it. Once you are, hug the cavern wall to the left instead and begin rolling until you are through the hole; I stopped rolling and got hit. Once you've made it through, jump down where you'll find a Site of Grace you can rest at, before running through the tunnel until you've made it outside.
Alternatively, leaving while crouched (something I didn’t do in the video) shouldn’t trigger the foe that shoots spikes, which should allow you to leave without taking any damage.
I recommend teleporting out of the area since Carian is way too high for you to beat right now; any enemy you find there will absolutely obliterate you. Leave Carian (and the Sellia Crystal Tunnel) for later, when you're supposed to face it.
I hope this was useful! I had to run around like a headless chicken and had the misfortune of finding the boss instead of the exit, meaning I got beat around like a ragdoll, so I decided to make a guide to prevent anyone from struggling with the same.