On a different note:
Mundane characters can absolutely explore a wreck without magic. Diving bells exist.
But DnD worlds are magical. The desire to carefully avoid ever having it be true that the best solution to a problem is magical is like making a science fiction game where it's never the case that technology is the best solution to a problem. It's not a reasonable requirement.
If you want less magical dnd, there are 3rd party options, like Adventures in Middle-Earth. That product is well balanced within itself, and magic users are by far the minority.
But for me, even if I'm playing a swashbuckler rogue with no magic of their own, I'm playing in a magical world where sometimes the diving bell is replaced with a ring of water breathing that you can buy from the shipwright that attaches to the mast of your ship, and allows you to breath water and ignore the pressure of the deep for a certain amount of time, x/day.
Because the literal physical world itself is magical.
I keep running into this in my own system as well, where one of my friends and fellow designers will point out that there's nothing stopping every character from gaining magic of some kind, and I'm just like..."Okay? So what? Why wouldn't every Wise (a term which here means, someone who knows about the supernatural) person find or learn magic of some kind? If someone wants to play the fantasy version of a Luddite, they can, but the game doesn't need to encourage it."
Diving bells may exist, but I suspect many campaigns don't have them. And a diving bell lets you see the wreck, not explore it. SCUBA gear on the other hand would let you explore it. It would be potentially more dangerous than using magic but that's OK! It moves the necessity to a convenience.
Having the world have had this question asked and a reasonably priced answer determined (like the mast ring) is great! An herb that grants water breathing for a hour would also work great. I just think the game would be better off with some strong systems/advice for DMs to include such in their worlds through faction support, incidental magic, or non-magical equivalents.