There's only place on the planet left to discover, according to Sir David Attenborough.
"The ultra depths of the ocean is the last frontier," explains the veteran broadcaster. "There's nothing else we can't do - it's the only missing piece of the jigsaw, which I quite like. But I thoroughly expect we'll get down there one of these days."
And yes, he should know, after spending six decades bringing the most remote spots of the earth and its disarming inhabitants to our screens.
Although everybody immediately thinks of the gorillas as one of his most glorious television moments, Attenborough himself won't be called on a favourite - "too many to mention" - and reveals equal delight at the technical challenges he's overseen along the way, including making BBC2 the first British channel to transmit in colour, and the study of nature, first in digital film and, more recently, in 3D.
Sir David spent the best part of a decade during the 1960s and 70's inside the executive walls of the BBC, firstly as Controller of BBC2, then as Director of Programmes, before getting full-time back in front of the camera. He remains justly philosophical about the recent trials of his long-time employer, but maintains a mantra the top brass could do well to pin to their office walls for times of trial... "The BBC was first banned in 1926 by Winston Churchill, and ever since then, at regular intervals, it's had challenges and criticisms of its position, which is completely reliant on the trust of our viewers. It's very simple - we just have to make sure we're always working to retain the trust."
He's similarly evangelical about the challenges facing the natural world, having been at close quarters to regions suffering the effects of global warming on the world's most stunning landscapes. He puts it down to one word - "over-population".
What about when he's faced with the fruits of his expeditions, curling up in front of Blue Planet, Frozen Planet and dozens of other programmes that have come to be part of our national consciousness, can the sights and sounds inspire the same wonder as in us, or is the veteran broadcaster too aware of the technical machinations?
"By the time it gets to the screen, I've seen it far too many times to be surprised," he explains. "But put me back in the natural world, and my appetite for wonder is endless."
Attenborough: 60 Years in the Wild - a three part series revealing how documenting the natural world has changed during the 60-year career of one of the most important naturalists of the last century - is available now on DVD and Blu-Ray. Watch the trailer below...
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