One of the most joyous pieces of television you are likely to see this year, or any year, involves Sir Michael Palin, surely our most adventurous octogenarian, picking his way, barefoot on the slippery stones, behind one of the most spectacular waterfalls in the world – El Hacha in Venezuela.

Behind the full force of nature, the man who had heart surgery five years ago stands for a moment, catching his breath, soaked from the spray but also exhilarated to the core. 

'I'm 81! I shouldn't be here! I should be in bed,' he yells to the world.

He may have made a second career as an intrepid TV traveller, but today Sir Michael – who has turned 82 since returning from this epic trip to the South American country – admits to an uncharacteristic frisson of fear as he decided whether he was up to the waterfall challenge. 

'I don't normally like to go on about age, but when you're at a stage in life where people give up their seats on the Underground for you, then you do have to be a bit careful about what you put your body through. 

'This involved going barefoot into a thunderous waterfall so I did have to think, "Do I want to do this?" because if I'd stepped on the wrong stone and gone a*** over t**...'

Yet he not only did it, but he clearly loved every minute. 'To not only do what was required of me but to be excited by it was tremendously reassuring,' he smiles. 

'So I came back feeling a lot better because before you go you have doubts and worries about whether you can still hack it.'

It's official, then. Sir Michael Palin can still hack it. 

His latest TV adventure saw him spend three weeks in Venezuela, which by rights should be one of the most visited countries in the world, given that it boasts stunning beaches, the Andes mountains and the Amazon rainforest. 

Why isn't it firmly on the tourist trail? Because it's also one of the most dangerous countries in South America. 

Soaring inflation and high murder rates have led to more than seven million people fleeing the country in the past decade.

With President Nicolas Maduro at the helm, international observers say the country is fast becoming a totalitarian state.

Enter nice Mr Palin, previously of Monty Python fame but more recently king of the travel documentary. 

He's made an art of making compelling TV from difficult places (in recent years he's been to North Korea, Iraq and Nigeria), but this trip saw Sir Michael and his team get apprehended by gun-wielding officials while trying to film at the site of a statue of former president and revolutionary Hugo Chavez. 

It sounds quite heavy – and scary – stuff, although his recounting also adds a layer of bemused humour.

'They took all of our equipment,' he says. 

'Actually, not just the equipment. Anything that was in a bag was photographed by military intelligence, right down to our dirty laundry. I mean, what military intelligence would get out of my underpants, I really don't know.'

He titters now, and tells me he became aware that the guards were Googling him. 'At one point they found a YouTube video where John Cleese and I were discussing The Life Of Brian with the Bishop of Southwark.'

From their reaction it seems they weren't Monty Python fans, and were struggling to make sense of what they were watching. 

'They all looked a bit baffled behind their helmets and visors,' he laughs. 'The whole thing was very Pythonic, but eventually strings were pulled and we were allowed to carry on.'

He thanks his lucky stars, he says, that his job requires a degree of risk-taking. 'I feel very lucky to be able to go off piste, away from health and safety regulations and people saying, "You can't do this, you've got to hang onto this rail."

'There are no handrails in Venezuela. It's a dark, strong, weird, wonderful, noisy place. I probably broke tons of those rules. 

'But that's what I like about travelling. Wherever I've been in the world, you have to deal with a new set of circumstances and it tests you both physically and mentally.'

Does he think we mollycoddle our octogenarians too much in this country? Yes, it seems. 

'There's a feeling you're reduced to some incapability over a certain age, that you must basically just sit in your chair, that you can't have boiling water in your coffee because it might scald you. You can forget all that when you go travelling. And that's what I do.'

There is a moment in this documentary, though, when he utters the 'r word' - retirement. 

Sitting on a lounger by the Canaima lagoon, he surveys the stunning vista before him and says he could retire here. 'It gave me a glimpse of what another life could be,' he says. 'But I know it's a life I wouldn't want, really.'

He's good mates with Sir David Attenborough and says he thought of him while deciding whether to take on the waterfall. 

'There aren't that many of us still doing pieces to camera in our 80s but then of course there's David Attenborough. 

'He's 99 and still doing pieces on windswept cliffs or in a swamp. Now that is the man to make us all work harder.'

Both men threw themselves back into their work when they lost their wives. Sir Michael has only been a widower for two years. His wife Helen – mother of their three children – died just days after their 57th wedding anniversary. 

She had been ill for several years and he says that 'for a couple of years I was really a carer'. His job was to make sure Helen got out for a walk every day, 'even when she didn't really want to'. 

And to make her laugh? 'Oh, yes. And she did laugh, mostly at my attempts at cooking. She enjoyed my incompetence.'

He talks about how much pain she was in towards the end, and says: 'I don't know where she found the bravery for that.' 

Does that make him wish for a quick death? 'In some ways, but at the same time she had time to see the grandchildren grow up, which she treasured.'

Sir Michael is the least maudlin man you could meet, but still the loss here is palpable. Helen always shooed him off on his adventures, and he started to film again after her death 'because she would have told me to. 

'What is the alternative? Sit at home?'

Helen was never hugely interested in his tales of derring-do and he tells the story of once calling her from Mount Everest, only to hear her ask about when the plumber was coming. 

Every year he still makes an effort to holiday with the family, 'even though there is the deep sadness of her not being there. But her spirit was very much about just getting on with it, so it's a way of honouring her.'

How has he adjusted to life without Helen? 'Well, you have to reorganise your life. It's been "we" and "us" for 60 years, now it's just "me" and "I", which is hard to adjust to, but the way I've come to think of it is that we had a great relationship, which just continues after her death. Having something to do, work-wise, helps.'

He's lost other good friends too because that is the curse of being as fit as a fiddle in your 80s. 

'Terry Jones [his fellow Python], Neil Innes [the writer and musician] and Tristram Powell [the TV and film director]. It's rather like a cast of characters, you look around the stage and then suddenly it's a bit more empty. 

'That's difficult because these were people I would go to because they know me and I know them, so there aren't that many shoulders to cry on these days.'

What will he do with his wife's possessions? That's a work in progress, and most of Helen's things remain. 

'I'm not hanging on to them because I never want to let them go, but for the past two years I've kept the house as it was,' he says. 

'I don't want a lot of empty shelves and cupboards. I don't want empty hooks where the scarves might have been. 

'I'd rather have the scarves there and the dresses in the wardrobe, and the feeling that this is still "our" home. It would be very strange to de-clutter my wife out of my life. I'm not ready for that yet.

'I've had very many emails and letters from people in similar situations. No one will ever feel the way you do, but there are certain aspects, like the hopefulness of carrying on, that can help.'

So he will carry on. 

'I still think the world is an amazing place and I'm lucky because I don't have to just read about it in books and watch TV. I can get out there and make the TV and write the books.'

So where next? That will depend on the success of this series. 

'You're only as good as your last programme and at the end of the day, we're entertainers – not explorers, not scientists. 

'Entertainers. If the ratings are good I will have done my job. But will there be another trip? Even though I'm getting on a bit, I'm up for it.'

Michael Palin In Venezuela is on Channel 5 later this month. The book of the same name is published on 25 Sept by Hutchinson Heinemann.