Ivan Trifonov successfully landed a balloon at the bottoms of the Mamet Cave in Obrovac in the Velebit nature park.
The flight took 25 minutes and Trifanov flew a smaller-than-usual balloon that meant he had to sit on two gas cylinders framed by iron pipes rather than a traditional basket.
According to Stuff.co.nz, the entrance to the cave was just 60 metres by 70 metres.
Trifonov, who holds four Guinness World Records for hot air ballooning and is the first person to balloon over the South and North Poles, told the Guardian: "I don't believe this is going to be repeated by anyone ever again."
There's a challenge if ever we heard one.
Ivan's flight was supported by the Croatia Tourist Board, who uploaded the video to YouTube and wrote: "Exactly 10 years after the recording of Felix Baumgartner's base-jump in the Mamet Cave went around the world, this abyss on Velebit Mountain became the scene of another incredible daredevil venture.
"Ivan Trifonov, a seventy-year-old Austrian with a Croatian passport, was the first man to try, and succeed in flying a hot-air balloon underground.
"This experienced hot air balloon pilot is already a proud holder of four Guinness records, and flying into the Mamet Cave, touching its bottom and successfully flying out of the cave is likely to be his fifth record, since no one has ever done such a thing before.
"For flying underground, Trifonov had to use a hot air balloon specially designed for this unusual, and probably unrepeatable venture. His balloon was smaller than usual, and the brave pilot set on two gas tanks linked with steel pipes, instead of a basket."
Up, up and away! Beautiful balloon trips all over the world
World's first underground hot air balloon flight takes place in Croatia
Take in the wonders of the Flinders Ranges, the oldest mountains of Australia, courtesy of a luxury balloon ride organised by eco holiday company Rawnsley Park Station. The journey takes in incredible scenery as you waft over Wilpena Pound, a remarkable natural formation in the heart of the Flinders. Price: AUS $350 per person, with discounts for children aged under 16.
Go on a game-viewing adventure in south west Kenya for a safari with a difference. Suspended in a basket beneath the rainbow-coloured canopy, you float silently above the plains, forests and rivers of this enormous game reserve. The ride is followed by a champagne breakfast, cooked wherever you land – all very romantic. Price: from £265 with Bridge & Wickers.
Let the mountains rise up to meet you on this a ride from Marrakech. Best of Moroccooffers a morning's ballooning experience including transfers from and back to your hotel. Price £336. A four-night stay in Marrakech is from £393 per person staying at Riad Laora – a charming boutique property with a small heated courtyard pool in the heart of the Medina.
See the rolling Tuscan countryside from the air, going wherever the wind takes you. Head north over the Crete Senesi and Siena. Float westwards to gaze over canyons and valleys, south to Pienza and the Val d'Orcia, or east over wooded hills and into the Val di Chiana. A champagne toast back on the ground will help bring you gently back to earth. Trips cost from £212 per person with Tourdust.
Take a relaxed approach to sightseeing with a balloon ride over Melbourne, one of the only cities in the world to offer hot air balloon tours. Global Ballooning organises sunrise tours complete with champagne breakfast that promise to be make for an unforgettable experience. For more information on Melbourne and balloon rides, go to Visit Melbourne. Prices start at 350 Australian dollars per person.
The Namib-Naukluft National Park is home to the world's highest sand dunes, vast plains, mountains, sculptured canyons and, in total, 50,000sq km of space and silence. Watch the dunes turn fiery orange giving surrounding peaks take on an ephemeral glow with a glass of fizz in your hand. For more details, check out Namibia specialist Expert Africa. Prices from Â£392 pp, including the champagne breakfast. A ten-night safari including the hot-air ballooning costs from Â£2,317 pp.
Balloon Flights Spain arranges hot air balloon rides in Spain, Portugal or Palma Mallorca, Majorca. From arid deserts to rolling plains, crystal clear coves to untouched nature reserves, you can take to the skies in style. Toledo, Seville, Granada, Cordoba and Ronda are just some of the famous cities you can soar above them. Prices start at 195 Euros per person.
Every November in the town of Pushkar in the northern Indian state of Rajasthan, a huge cattle fair with camel races takes place. Tourists come from all over the world, and can take balloon rides over the banks of Pushkar Lake, a popular Hindu pilgrimage spot. Prices start at around £180. For booking enquiries, visit Skywaltz.
Take a trip at sunrise to explore the glorious olive groves, countryside and castles of the beautiful Italian region and enjoy a champagne breakfast as you glide. Trips start at 240 Euros per person for a small group, or honeymooners can book a balloon a deux for around 850 Euros from the Chianti Balloon Port at flyballoon.it You can also opt for ballooning lessons with the Associazione Aerostatica Toscana to obtain a private pilot's licence. For accommodation, visit summersleases.com
...or Cornwall, or Dorset, or Somerset or Wiltshire, on a balloon ride organised by UK specialists Aerosaurus Balloons. Take an Early Bird flight at dawn on a weekday for as little as Â£99 per person from a choice of locations - and you get champagne and a commemorative flight certificate thrown in for good measure.
Hot air balloon rides over the Masai Mara and Namib desert at Sossusvlei are a once-in-a-lifetime experience when you organise your trip through African specialists AndBeyond, which offers luxury accommodation in some of the most diverse wildlife areas of the world. Explore the foothills of the Nubib Mountains and the incredible sand dunes at Soussusvlei (some of the highest in the world), or watch the great wilderbeest migration in the Masai Mara - contact them for individual trips and prices.