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 Saturday morning, Monday afternoon's cross-country test should separate serious medal contenders from the rest. 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 on Thursday.
And more course walks were planned for Friday 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.
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. "
The British team starting order was announced on Friday afternoon. Wilson and Opposition Buzz will be the first British combination into the dressage arena. Wilson will be followed by King, with Phillips in the third team spot, Cook fourth and Fox-Pitt fifth.