At its heart are the Kīlauea and Mauna Loa active volcanoes. The Crater Rim Drive passes steam vents and the Jaggar Museum, which features volcanology exhibits and a viewpoint overlooking Halema'uma'u Crater. Thick ferns mark the entrance to the Thurston Lava Tube (Nāhuku). The Chain of Craters Road weaves over lava.