The cave you're exploring doesn't have a name. It's not actually a cave but you don't know that, it looks just like one. You're actually being slowly digested in the cave, as if it was a giant slumbering monster. The cave walls actually move a little like breathing if you put your hand to it and focus very carefully. No matter if you turn around or keep going forward the walls will keep getting narrower and slowly crush you to your death. That's why it's closed off. Your friend is paranoid.