Amazing landscape. When you are in the core of the dead volcano, it's like you are on a completely different planet. Side note - the rabbits out here are the largest I've ever seen... like, sheepdog size.
One of the best surprise road trips my Dad ever took us on. Make sure you have sturdy shoes, dress in layers, & bring a decent light source. If your are clumsy like me, you might also want to wear a helmet.
I'm not a religious person, but this place certainly placed me in a spiritual state of mind.
Call ahead to make sure it's open when you plan on visiting & try to plan a visit around a festival at the park to have even more fun.