Ignoring part 2 of the movie and just assuming part 1 was a stand alone feature.
Were the monsters real, or were they just the main characters suppressed rage against her friends who she blamed for her husband and daughter’s death?
The original ending makes me think the main character was delusional.
Also I’m watching this right now. Before they go into the cave one of the women starts talking about all the dangers of caving. She mentions auditory and visual hallucinations, paranoia, panic attacks, disorientation. Sounds like what the characters went through.
Great movie. It’s a long time since I saw it, so I can’t remember all the details, but I felt something like that was hinted at. The title itself hints at “descent into madness”. But I don’t think we know for sure. Better to leave it unanswered than a soap-opera-esque reveal that it was all in her mind?
Incidentally, from Wikipedia: