As I’ve seen it, although I don’t remember which comics specifically, he stumbled upon it as a young boy so his parents would’ve built it or it’s somehow naturally occurring

@Jokerobsessed17 I think the question was how did all the infrastructure get built into the cave, not how did the cave itself come to be.

There have been several attempts to rationalize the Batcave - underground railroad, old mine, abandoned subway station. In the end, it's just something you're going to have to accept.

I like to think he started out small and then had Superman or Green Lantern help or something.

Most of the comics I have seen it was extensive before him taking up Dick Grayson and before joining the Justice League. I know there was some book out there saying he had workers live down there and build it but don't think that was Canon. That sounds like that would create a lot of problems.

This is based on absolutely nothing but my own headcanon, but I like to think that he just payed a bunch of workers an overwhelming amount of money to not talk about it, and I´m talking about enough money to set them for life, which is possible since he appears to have an endless supply of money

For decades, I've been curious how the heck Bruce got that giant penny & t-rex statue into the batcave! Those are in the background so often. And isn't there a giant Joker card too? Why would he even keep that stuff??