I don't think I would have wanted to be a miner, either.
I have seen photos of parts of Carlsbad Caverns; and yes, it does contain large chambers. Most cave passages are of at least reasonable walking-size, and there are a few places where you would need a lamp with a powerful beam to illuminate the roof and wall from the centre of the passage or chamber. On the other hand, yes there are caves that involve almost all crawling on hand-and-knees or flat-out. I can't take too much of that these days; but no-one really enjoys such places even if not claustrophobic.
A show-cave, such as the tourist parts of Carlsbad Caverns, uses only the areas easily accessible to non-cavers, and if possible involving minimum alteration of the cave other than providing appropriate concrete paths or steel walk-ways; and of course installing lighting.
Longest time I have been underground was about a day and a half I think, involving actually camping down there overnight. I've also been flooded in overnight. The three of us were not in danger from the water directly as we were beyond the flooded section, but the cold would have been a serious problem if we'd not managed to come out when we did, after the water had dropped to a safe level. Usually, most caving trips last just a few hours. Every cave is different and how much time you take negotiating it depends on so many factors it's not easy to answer that question. What we normally do though, is estimate the time we'll come out, from experience, and leave that time with a reliable surface contact.
Most caves are inland, away from the sea, but there are a few close enough to be affected by the rising tide in one way or another. A friend found one only a few miles from my home, that floods at high tide, apparently from inside; but the route back from it would probably be more hazardous when submerged. The Blue Holes of the Bahamas and I think Florida, are entrances to caves now lying well below sea-level, because they formed during Ice Age glaciations when the sea level was much lower than now. I believe archaeological remains have been found in a few of them.
As for "dark narrow", well, yes, however narrow or wide, once away from the limit or daylight penetration they are totally dark. No light at all. The only natural places on Earth that are as dark as caves, are the ocean deeps.