Operation Grand Canyon on the Beeb.
The Grand Canyon is pretty much impossible to walk along, the only horizontal part being filled with the river. And the river is fairly challenging, with huge rapids and vast distances between any realistic pullout points.
So it is not surprising that as late as 1869 the entire valley was a blank hole in the maps, entirely unexplored.
The first expedition was led by Major John Wesley Powell, a hero of the American civil war who had lost his right arm at Shiloh. They took three rowing boats of a more or less standard design, stuffed them with supplies and started out. It took them months, partly because they had no idea what to expect and had to recce every rapid before risking their delicate boats. Many times they emptied the boats and let them down on lines, following on foot. It must have been heart-wearying.
Snow and his merry men try and reproduce the conditions as far as practical, but they are led by experienced river guides (one with epic Victorian-style face fungus that would have been entirely at home on the original expedition) so progress is much quicker.
They are also followed by a fleet of safety boats and camera crews, but refreshingly Snow comes clean about this right at the beginning. Surprisingly, despite the concern for safety, they set off for the rapids without having practiced rowing at all - timing is rubbish. I would have thought that was a rather significant hazard.
At least they had a tin of tar on board. Powell had to make his own. They had to climb to the top of the canyon to find suitable wood, burn it and extract the tar - an incredibly time-consuming process. What men!
The BBC has issued a free ebook to go with the series. Recommended.