Undara The next day we toured the lava tubes. They are immense caves that were only recently discovered and explored. Here's what a lava tube is in case you ever come across one. When this one volcano erupted a gazilion years ago the lava flowed slowly across miles and miles of this area. It flowed through into a deep river and followed that path. As the lava flowed through the river it hardened on the bottom sides and top allowing the lava to continue flowing inside like a pipe. After the lava stopped flowing it emptied out the pipe and left these tubes. Then after earthquakes the tops collapsed in areas and these are the caves we went into. These are the largest and longest lava tubes in the world. You are here...