Of all the videos out there, this one captures why I cave dive better than any other, I think:
Reflections - Through a Mirror Darkly - YouTube
When I was a kid, I loved bouldering up streams . . . even though one rock is very like another, there was always the lure of "What's around the corner?" One might find a waterfall, or a stunning view . . . or it might be more rocks. Cave diving has a lot of that. What's around the corner? Mastodon bones? Huge rooms? A slope of intricately curved and woven travertine dams? There is a place in one of the cave systems in Mexico, where you have been swimming for 15 minutes through very decorated but very dark passage. The rock is tannin-stained, and the water has an eerie, greenish cast. Suddenly, you swim over a rock rib and down through the halocline. Once your vision clears, you are in an ENORMOUS hallway, maybe forty feet high and about the same wide. The vertical walls, ceiling and floor are pure white, and the water is a deep, cobalt blue. The walls are decorated with draperies of golden flowstone, and the floor is punctuated by elegant pillars. The sudden contrast makes you gasp, the first time you see it.
The ONLY thing in the movie Sanctum that was real, was the team coming through that restriction in the beginning, and bursting out into that amazing room.
When you add the very defined technical challenges of doing cave diving well, the romance of seeing places few people have or will ever see, and the camaraderie of people who cave dive, you add to the appeal.
But in the final analysis, it's what Karen said: Cave diving requires you be utterly present. Drenched in the moment, you are insulated from every other concern. That type of concentration is very addictive.