Over the course of 70 million years, rainwater progressively carved into limestone formations under Barra Honda Peak, creating a cave system today that is one of Costa Rica's most underrated natural sights.
Barra Honda National Park's cave system has, even today, only been discovered about halfway, but scientists have found bizarre species living in the darkness, including a completely blind salamander and fish that have never seen the light and live uniquely in the Barra Honda caves. There's also a cave that is home to 5,000 bats!
Actually, the hill under which the caves rest was once an undersea coral reef, hence the incredible formations you'll see when you visit this strange place, including stalactites and stalagmites. On your journey, you'll pass through the cave of organs, the fried egg cave (so named because the geological formations here look like your breakfast) and see formations that resemble popcorn, grapes, shark's teeth and flowers.