Spelunker's paradise: hidden caves that are unlike anything you have seen before

If you are seeking a cool adventure, perhaps there is nowhere better to look than beneath your very own feet. I am not talking about trying to crack through the earth’s crust with a bucket and spade. Rather, encounter mystery, stupefying beauty and an adrenaline rush like no other by exploring some of our planet’s most exciting caverns. Some are a unique challenge just to be able to enter or traverse; others are submerged, composed of ice or crammed with spectacular geological features.

Whether you are in it for the sheer thrill of it or for your Instagram feed, however, keep in mind that physical fitness is a big part of these cave adventures. The Plura Cave dive, for example, is where excitement, a sense of danger and an ethereal splendour collide. Situated in Rana Municipality, in northern Norway, it is the deepest cave in northern Europe. One of over 200 grottoes in the same system, it only became conceivable to dive in this particular one when Lake Kallvatnet was damned in the mid-1960s.

The first section of this about 30-metre-deep limestone and sandstone layered hollow is manageable by all levels of divers. But the second part, which sinks down to over 90 metres, is only for the highly-skilled – a pair of Finns lost their lives here in 2014 – so being physically fit and technically skilled are essential. The scenery is similarly imposing – expect slender craggy passages and massive boulders and be aware that you are not alone – creepy invertebrates such as enormous mites and spiders also populate this typically two-to-six-degrees Celsius aquatic milieu.

Those who are prepared to take on these gruelling experiences, however, are rewarded with both an adrenaline surge and a view like nothing seen before.

The Waitomo Caves, for example, wouldn’t be out of place in an Indiana Jones movie. Located in the King Country region of New Zealand’s North Island, amid verdant scenery, the hollows were formed out of Oligocene limestone more than 30 million years ago. It is possible to do a nerve-jangling 20-minute, 100-metre abseil into the heart of this immense sinkhole (alternatively, you can view it without rappelling).

Once you hit terra firma, one gets plenty of time to explore (the whole excursion takes roughly four hours). Expect the ceaseless whoosh of the Mangapu River, and be entranced by the speleothems and the spectacular sight of the flickering bioluminescence of thousands of glow-worms, which light up the cave like stars in a sky.

The Eisriesenwelt (German for “World of the Ice Giants”) ice cave is similarly picturesque. The largest of its kind in the world, it offers a totally different underground experience. Within its interiors, the frozen structures are so mesmerising, it is easy to believe one has strolled onto a Walt Disney film set. Situated in the karstified Tennen mountains (around 40km south of Salzburg), this place was discovered by the natural scientist Anton von Posselt- Czorich in 1879. Nowadays, visitors are able to catch a cable car up to this hollow and get a 75-minute guided tour of its monumental innards, using an old-fashioned lantern (the season runs from May to October).