Visit Natural Bridge by day to see a unique waterfall or after dark to discover the park's amazing glow-worms. While travelling through Numinbah Valley, take in the commanding views of the impressive cliffs that line either side of the valley, this landscape was formed by the Tweed volcano some 23 million years ago. Natural Bridge is an example of water's tremendous power. The hard basalt rock bridge we see today was once the lip of an old waterfall. Its base gradually eroded by swirling waters into an undercut cave. Rocks in the stream bed above swirled around to drill a pot-hole, which gradually deepened and broke through to the cave beneath. The creek fell into the cave and then enlarged it further.