The Tour comes out of the final rest day and begins what will be the most decisive stages of the race. With three straight stages in the Pyrenees Mountains and then an individual time trial, there will be many opportunities for riders to move up in the standings, and to make a mistake or have a bad day and slip down as well.
<Edit: I wrote this before stage 16 started>
Stage 16 is the first stage in the Pyrenees. By high mountain stage standards, it is relatively easy with a few rolling lower climbs followed by a single HC climb. The summit of the climb is 20km from the finish, so it's not a great choice to gain time for the top guys since any effort spent opening up a gap may be wasted as riders behind come together and use their collective aerodynamic advantage to close gaps down. However, riders with top 10 ambitions looking to move up from further down may try to sneak away in a breakaway and make some time but still not threaten the leaders. This should be a relatively calm stage, but if any of the favorites show signs of having an off day (as can often be the case coming out of a rest day), all bets will be off.
Stage 17 is what I would consider the Queen Stage, or the hardest stage of the race. With 3 cat 1 climbs in quick succession followed by the monster, 10km/8.3% HC climb to the finish line. This will be a dangerous stage and with so many tough climbs, the peloton will likely keep things together as much as possible. Any breakaway will be guys that are well, well, down in the GC, and even then, they will be kept on a short leash. Riders like Joaquim Rodriguez and Rafal Majkal, who are tied in the King of the Mountains competition will try to jump ahead and duke it out for the points at the top of the first 3 climbs, while the GC contenders will stay together and keep their powder dry for a big showdown on the final climb.
While Nibali has looked unassailable, the climbs of the Pyrenees are quite different than those in the Alps and Vosges. The climbs are steeper, the pavement is worse and the descents are more tight and technical. Nibali, and the others chasing him, will have to show they can handle the terrain after 2 weeks of hard racing, as well as staying safe on the descents.
Stage 18 will be the last mountain stage. For natural climbers, it'll be the last chance to make hay. Everyone else will looking to survive the last big obstacle to making it to Paris. Two, back to back HC climbs are on the agenda for the stage, first up the 17km/7.3% Col du Tourmalet and then ending on top of the 13.6km/7.8% climb up to the ski resort, Hautacam. How this stage will shake out will largely depend on how the previous stages have unfolded. With only the individual time trial left to decide the overall GC standings, every rider will know exactly the time gaps they'll need to reach whatever goals they have for the race, be it winning, podium, or top 10. If I had to make a guess, it would be that the two French riders currently in 3rd and 4th will use this opportunity to move up, if they haven't already. Both have said the climbs of the Pyrenees suit them well and neither are proven time trialists. I would expect these two to jump ahead and fight it out for the stage win while trying to pad time on guys just behind them.
Stage 19 offers a bit of an opportunity to regroup and recover after the mountains and before the individual time trial. The GC riders will be hoping for a calm day, but for the sprinters and their teams this will be one of the last opportunities for a stage win. Peter Sagan has had the green jersey (awarded according to points given at flat stage finishes and intermediate sprint points) sewn up since week one, but he has not yet won a stage and coming in second with frustrating regularity. This stage will be his last chance, the sprints of the Champs-Elysées are better suited to the pure sprinters like Marcel Kittel. With a small climb near the finish, Sagan will put his team (Cannondale) at the front and drive hard in an attempt to shed the sprinters who can't climb as well as he can. Hopefully, he can keep a teamate with him in the last1km as a sprint leadout, something they haven't been able to do before, and finally get a win.
Stage 20 is the only individual time trial of the Tour this year. Dubbed "The Race of Truth," riders will complete the 54km course alone against the clock and wind. After 5 mountain top finishes and countless mountain passes, the tables will finally turn for GC contenders like American TeJay VanGarderen who excel in the discipline. The two French riders currently sitting ahead of him are not noted time trialists and he can gain a minute or more on them. If he managed to keep it close through the Pyrenees, this stage will be his opportunity to vault himself onto the podium. Nibali and Valverde are both good-decent time trialists, so they will likely hold serve barring crashes or mechanical issues. For the stage win, my money is on Tony Martin, world time trial champion three years running. He has been a beast this year, already winning a stage and constantly on the front working for his team, Omega Pharma Quickstep. The question is whether or not he'll have anything left. He'll have hauled himself through 3 weeks hell just for a shot at this stage, so motivation will not be an issue.
The Tour concludes on Stage 21, the traditional ride into Paris from and 8 laps around the famed Champs-Elysées. Traditional also dictates that the riders vying for the general classification do not attack each other on the final day. This allows for champagne toasts and victory cigars in the leisurely ride into Paris. For the sprinters, however, the story couldn't be more different. For them, to win on the Champs is the absolute pinnacle of their discipline, and all the suffering through the mountains (which, with the exception of Sagan, the sprinters are allergic to) was just for a shot at this stage. They and their teams will make huge efforts and take huge risks at a chance to cross the line first.
Marcel Kittel won here last year and will be the odds on favorite. I'm going to go out on a limb and pick Alexander Kristoff for the win. Kittel has seemed to lack his normal pop recently, maybe worn down by a couple crashes and hard days in the bad weather and mountains. His team's organization hasn't been stellar either, something that'll be crucial in the chaos leading up to the finish line. After two close stages in 2nd place, Kristoff finally broke the seal on stage 12 and followed it up with another on stage 15. He seems to have survived the mountains the best of the sprinters so far and his team has been a dark horse this year, always seeming to come out nowhere at just the right time to place him in good position. Either way, it should be quite the spectacle to wrap up a crazy year at the Tour.