Intro:

Ivan Trifonov flies a hot-air balloon in to the 206m deep Mamet Cave in Croatia.

Script:

Hot air balloons are designed to rise but this one is descending.

Dropping in through the 60m wide, 206m deep Mamet Cave in Croatia was Ivan Trifonov's idea of fun.

The Austrian balloon pilot was the first man to try - and succeed - in flying a hot-air balloon underground.

25 minutes later, Trifonov returned to the surface with a potential world record.

SOUNDBITE: (German) Ivan Trifonov, balloon pilot:

"This was a very difficult thing to do. A very difficult project. One must have the right balloon, the right weather and the right support… It was very hard and I don't think anyone else will ever repeat this venture. I sincerely doubt it."

Trifonov hopes his journey to the centre of the earth will be recognised as a new Guinness world record, which would take his grand total to five records.