Caves are generally quite dark places, so it does make them difficult to see. But bear with us and squint through the gloom, as there are some astounding caves around the world that you really must see.
The featured image of the Cave of Crystals is courtesy ofÂ www.laventa.it.
Waitomo Glowworm Caves, New Zealand
Glowworms used to be our only way of illuminating caves for millennia until we finally got round to inventing energy-saving lightbulbs.
The best place to see natureâ€™s LEDs is Waitomo, where tours culminate in a pitch-black boat ride with nothing but thousands of the little blighters guiding the way.
Cave of the Crystals, Mexico
A cave full of massive selenite crystals can be found attached to the Naica Mine in Chihuahua, giving people the opportunity to walk around a place that makes them feel like the villain in a James Bond film.
Be prepared to get a geology degree though - the 50C temperatures inside mean tourists rarely get a look in.
Wieliczka Salt Mines, Poland
Ok fine, itâ€™s a mine - but a mine is really just a man-made cave so this remarkable spot near Krakow definitely counts.
Thousands of kilometres of tunnels and chambers have been excavated in Wieliczka over the centuries, with miners spending so much time down there that they carved out quarters, chapels, lakes and even a full cathedral hundreds of metres under the ground.
Itâ€™s probably also one of the few places in the world where tour guides encourage visitors to lick the walls.Adam Zulawski