I have mate back in 2008, it is absolutely stunning place, it is 64 km in length starting at about 4500m above sea level and finishing about 80m above. Beautiful scenery, you start up in the mountains in the snowline and pass through temperate jungle and end up not to far from the sea, but at a place with a pool.
It is not technical really, but there is a huge drop to one side and you can see all the cars and buses that have gone over the side in the bottom of the canyon. You can reach 30mph + and it is on a rough surface so the arm pump is the worst bit.
If you are going to do it, go with an american firm with decent bikes, we went with a local bolivian firm, paid for full sus Iron horse bikes and got there to find we had old Trek Hardtails, my back tire burst 62km out of the 64, i ended up dislocating my shoulder, pulling the head of my humerous off and having 2 screws in there, but one good thing about Bolivia the drugs in the hospital were good.
If you are that way it is a days bus road from Cusco where you Machu Piccu from.
I can send some pics of the place if you were interested in it.