World number one William Fox-Pitt believes the pivotal phase of London 2012's Olympic eventing competition promises a journey into unknown territory.
British designer Sue Benson's 28-fence cross-country course will challenge the world's best riders over six kilometres of testing, twisting Greenwich Park terrain.
Although the competition begins with two days of dressage, starting on Saturday morning, Monday afternoon's cross-country test should separate serious medal contenders from the rest.
A crowd of 50,000 is expected to watch riders tackle such imposing obstacles as the River Bank, East End Barrows, Chestnut Logs, Bandstand Rails and Observatory Turn.
Competitors - including the British team of Fox-Pitt, Mary King, Zara Phillips, Tina Cook and Nicola Wilson - were allowed their first glimpse of Benson's work yesterday.
And more course walks were planned today after the first horse inspection, which all five British horses - Lionheart, Imperial Cavalier, High Kingdom, Miners Frolic and Opposition Buzz - sailed through in Greenwich Park's main arena.
"The horses have got to be fit, absolutely, but the course is so unknown," Fox-Pitt said. "The terrain is fairly extreme.
"The first part of the course is going to be fairly frantic, but if you have got petrol in the tank towards the end of the course you could make up some time on the flat.
"But it is hard to know how much you are going to have left.
"You will be doing very well to be up on your minute-markers during the first part of the course, yet what we don't know is how far down on time you can afford to be."
The optimum course time has been set at 10 minutes, three seconds, with Britain expected to fight for team medals alongside Germany, New Zealand, Australia, France, USA and possibly Sweden.
"This course is going to be a first for many, which will make it a very exciting competition. It's a bit like Gatcombe without the galloping bits," Fox-Pitt added.
"There are a good few teams that will all probably have an equal chance of dealing with it. I don't think it is going to play into anyone's hands particularly.
"Had it been at Badminton, Burghley or Blenheim, then it maybe would have been Team GB-friendly.
"There are quite a few fences where you can't see what is coming, so you need to prepare to be slightly surprised. It's the sort of course that if you could ride around it twice, you would have a much better go second time around."
British team manager Yogi Breisner, in charge of his fourth Olympic campaign, feels that home advantage could assist what is a vastly-experienced riding quintet.
All five have enjoyed world and European medal success at various points in their careers, with Fox-Pitt and King boasting eight previous Olympic appearances between them.
"It doesn't really matter where you are, the expectation that you do well is always there," Breisner said.
"I think it will probably work for us here because it is nice for the riders to hear the crowds behind them. They are going to have tremendous support.
"New Zealand, Germany, France, USA and Australia are all threats, but I have been saying for six months now that the real outsider with a real chance is Sweden.
"They have got a very strong team here, and it will suit them down to the ground. They could do well.
"I don't think the British people should be surprised if we are a little bit behind after dressage. Hopefully, we will be able to claw our way back.
"We haven't got a team of dressage specialists like some of the other nations might have."
Germany, spearheaded by their brilliant reigning world and European champion Michael Jung, start as favourites, yet a New Zealand team containing double Olympic gold medallist Mark Todd, Andrew Nicholson and Caroline Powell on her 2010 Burghley winner Lenamore, could easily strike gold.
Todd, 56, is New Zealand's oldest Olympian at these Games, and he was in jocular mood on the eve of his seventh Olympics.
"Since I've been here I keep getting questioned as to what team I am an official for," he said.
"I keep getting on the bus and people say 'this bus is only for athletes'. I constantly have to say 'I am an athlete'."
"It's probably not quite the same as when we first went to Los Angeles in 1984.
"Andrew (Nicholson) and I were new kids on the block. We sort of ran round the athletics track, jumped the hurdles. We did this, we did that.
"We are kind of over that now."
The British team starting order was announced on Friday afternoon.
As expected, experienced cross-country pathfinders Wilson and Opposition Buzz will be the first British combination into the dressage arena tomorrow.
Wilson will be followed by King, with Phillips in the third team spot, Cook fourth and Fox-Pitt fifth.
Start times have yet to be confirmed, but it looks as though Wilson will be joined by King on Saturday, with Phillips, Cook and Fox-Pitt facing their dressage tests on Sunday.