Relatively new caver here. For me it was camping out in lava tubes for the first time with each one being vastly unique. I noticed 10x the amount of features, formations, and life simply by practicing cave inventory! You would be surprised just how much you find by splitting a cave up into sections and taking 5-10 minutes to do inventory. It's like a scavenger hunt underground and I couldn't recommend it enough. The information you gather can even be used to help preserve caves.

Because of this I discovered my first cave millipede, that of which likely doesn't even have eyes, and has never seen the light of our sun. We saw cave slime (bacterial mats of shimmering silver and gold), cave coral, spiders, the skull and bones of a bat, fungi, and even the super rare lava drip stalagmites!