Chadden Hunter / Entering the ice caves of Mount Erebus, Antarctica. Taken on location for BBC Frozen Planet series, 2009

Inaki Relanzon / Potholer exploring the Graller del Boixaguer cave, Montsec mountains, Pyrenees, Catalonia, Spain, May 2012.

Chadden Hunter / Stormy conditions outside the entrance to ice caves of Mount Erebus, Antarctica. Taken on location for BBC Frozen Planet series, 2009

Chadden Hunter / Entering the ice caves of Mount Erebus, Antarctica. Taken on location for BBC Frozen Planet series, 2009

Chadden Hunter / Entering the ice caves of Mount Erebus, Antarctica. Taken on location for BBC Frozen Planet series, 2009

Chadden Hunter / Filming around the extremely delicate ice formations in volcanic ice cave, Mount Erebus, Antarctica. Taken on location for BBC Frozen Planet series, 2009

Juergen Freund / Jovi Villareal inside a massive illuminated cave, Camarines Sur, Luzon, Philippines 2008

Juergen Freund / Jovi Villareal inside a massive illuminated cave in Caramoan, Caramines Sur, Luzon, Philippines 2008

Inaki Relanzon / Potholer in cave examining stalactites and stalagmites, Cova Meravelles, Bloc del Cardo, Benifallet, Catalonia, Spain, 1996

Inaki Relanzon / Potholer in cave admiring early formation of stalactites, Cantabria, Spain

Inaki Relanzon / Potholer wallking along narrow underground passage, Cova Lachambre, Ria, Conflent, Pyrenees, France

Inaki Relanzon / Potholer emerges from underground passage into cave with stalactites, Cova Lachambre, Ria, Conflent, Pyrenees, France