Punakaiki Cavern is a good stop just a short walk from the road near Pancake Rocks. You can park on the roadside car park but it gets full quicly so I recommend parking at the Pancake Rocks and walking along the coast to the cave. The entrance is easy to find and you can explore inside without needing any special gear. It does get dark quickly once you step in, so bring a headlamp or use your phone light to look around safely. The rocks are damp and a bit slippery in places, but it is a cool spot to wander and see the layers of limestone up close.

If you turn off your light for a moment, you might even spot a few glowworms on the ceiling, but it's best to look for them at night. It is not a long stop, maybe 15 to 20 minutes, but it's a nice one.