I took my kids to Lava River Cave in Sunriver when we were on vacation. It's pretty amazing. We hiked the whole mile under ground. We had a great time. Even my three-year-old went on the hike, and she did great.
She called it a "Mama Cave" because, you know, babies are small and Mamas are bigger, and it was a Mama cave, not a baby cave.
Also, she kept telling me there were monsters in the cave, and finally I said, I don't see any monsters. She said, "That's because the bats ate them all."
Ha ha ha!