A vast sea of cooled lava flows, some as recent as a few months. Acres and acres of black rock is twisted into bizarre shapes and encompasses surrounding towns, where you can see half-buried stop signs and remainders of houses that were in the path of the lava. You can climb over these flows, but be careful, as the rocks are uneven and bumpy. If you go towards the water, you may see the lava pouring into the ocean. In our case, the lava was rolling down the hillside.
In the park is Devastation Trail, which looks like a nuclear bomb exploded. It is "moon-like" in appearance, with dead trees scattered here and there.
There's also Thurston Lava Tube, an old, cave-like structure that once carried lava underground.
A book I found to be very helpful is the Book for Dummies Hawaii. I read this before going on my trip and it gave me a lot of valuable information.