Cave hobbyism

I've become curious about how many spelunkers are out there. One of the hobbies of me and my friends that very few people know about is cave exploration, or spelunking as it's called in the United States. It's a hobby that traces itself to my grandfather; he had a job post-WWII where he would venture into caves because there was a fear samurai were hiding in caves all across the Pacific. This turned into cave exploration skills which he passed onto my friends (less so me, I can "technically" do it for the visual enjoyment and do certain aspects better but consider it a safety red flag). I usually sit by as "reinforcements" outside a cave even though I do sometimes fancy some visuals.

There are a number of caves where we are, as it's one of the most erosion-rich regions in the world if not the most. Sometimes my friends discover things, either they take pictures or set them up for analysis. The activity can be so fascinating, caves are the opposite of open books and it's fun to "leave a mark" as you go, if that makes sense; it's like playing a video game in real life. Everyone talks about urban exploration, which is less insightful/legal and always involves places that were once sprawling anyways. Nobody talks about spelunking.

Any of you spelunkers out there? What caves have you been to? What's the most you've ever done, and what things have you discovered or brought back? And what did your experience involve?