At the end of the Road to Hana, a famous scenic drive on Maui, you’ll find the Hana Lava Tube, aka Ka’eleku Caverns. Unlike caves that can take millennia to form, these tube-like lava caverns can form very quickly, over just a few weeks.

As thick rivers of molten lava flow from an erupting volcano, the outside layer cools and will occasionally harden to form a tunnel. When the lava stops flowing, you’re left with a solid cylindrical tube of lava that can run for up to 30 miles.

Like many tunnels left behind after volcanic eruptions, the lava tube in Hana—the largest on Maui—shows all the geologic elements of lava flows that crust over. Among the many interesting things found in a lava tube are tube slime, extreme bacteria that live on the nitrogen; lava balls, which form much like a snowball rolling down a snowy hill; and lava falls, where a flow of lava has been frozen mid-fall.You enter the Hana Lava Tube through a hole in the cave’s ceiling that was created by gas punching through the crust, and explore the cavern along an unlit path. Don’t wander off though; the tunnels often have maze-like “braided” smaller tunnels in which it can be easy to get lost.