Four daring fundraisers have set off on a 6,700km trip that will see them row and cycle from London to Rio de Janeiro ahead of this year's Olympic Games.
Amateur rowers Johnny Keevil, 31, Jake Heath, 29, Mel Parker, 28, and Susannah Cass, 27, have prepared for three years for the trip, and some have even remortgaged their houses to fund it.
Their aim is to raise at least £125,000 for MacMillan Cancer Support, as well as highlight the legacy of the London 2012 Olympics as the hosting baton is passed to Brazil this year.
After setting off from the Queen Elizabeth Olympic Park in Stratford this morning, the Row2Rio team will cycle down to south Portugal where they will begin the row to Brazil.
When they reach the other side, they will cycle through part of the Amazon rainforest to reach Rio.
Mr Heath, a NHS podiatrist and former rugby player who came up with the idea with Mr Keevil, said: "We started talking in the pub about what we could do to carry on the London 2012 legacy and came up with this.
"I have stopped working to commit to this and have had to remortgage my house. I learnt to row and found that I am actually better at it than rugby.
"We are just ordinary people, not professorial rowers, so as well as raise the money for MacMillan we want to inspire people and show that anyone can do something amazing."
While on the water, each of them will take two-hour turns to row and rest, sleeping in small compartments at each end of the boat.
When on land they will mostly camp, but will pay for any accommodation themselves, and they have each put in around £15,000 to fund the challenge. However they are still looking for a main sponsor to name their boat.
The most experienced rower among them, Ms Cass, completed the Great Pacific Race in 2014 but says this will be her biggest rowing challenge so far.
She said: "I always seem to be looking for the next adventure. The hardest part will be getting used to being a bit bored for two hours at a time when you are just rowing.
"When we arrive, I think the thing I'll most look forward to is a good bath."
Charity fundraiser Ms Parker also has more rowing experience than her male counterparts.
She said: "I saw the team were advertising for a fourth member, so I applied and when we met we just got on really well.
"I'm not exactly looking forward to the "bucket, chuck it" toilet facilities we will be using - especially when the sea is rough - but I don't think it will take long to get used to it."
As well as solid bathroom facilities, the team will also miss out on proper food for most of the journey and will eat dehydrated ready meals.
Mr Keevil said: "When we reach the other side I'll be looking forward to a big drink and a steak - though after several weeks of reconstituted food, our stomachs might want to keep it simple at first."
A PE teacher by trade, he added: "Getting young people into sports is absolutely key, whatever the activity is.
"All of my pupils, their families, and my colleagues have been so supportive."
The team will be using Gopro cameras to take footage of their journey and will be working with a German production company to make a film to coincide with the beginning of the Rio 2016 Olympics.
They said they have arranged to go to schools and events to share their experience and continue promoting British sports.