1. Porte d'Envalira
The first critical climb of the middle leg of the Tour de France is set to be an absolute leg-breaker. That's because it comes right after a rest day, at the beginning of Stage 10: forcing the peloton to climb hard from the gun.
A rest day can do strange things to a rider's legs, so the advent of a 22.6km-long, 5.5 per cent climb - which is also the Tour's highest point at 2,408m - will not be filling many riders with happiness.
Look out for attacks designed to exploit any potential weaknesses in overall contenders straight away, and don't be surprised if GC hopefuls falter or even withdraw from the race.
2. Mont Ventoux
One of the Tour's most iconic climbs, the Giant of Provence has played host to many a decisive summit finish over its 65-year history in the race, with names as storied as Charly Gaul, Eddy Merckx, Raymond Poulidor and Marco Pantani winning on its slopes - the latter following a thrilling and controversial duel with Lance Armstrong.
It was most recently the location of Chris Froome's 2013 stage victory, which cemented his hold on that year's yellow jersey and was instrumental in handing him his first Tour.
The climb comes a little earlier in this year's race, on Stage 12, but promises to be no less essential to the outcome of the race. Every climber dreams of winning on the windswept moonscape of Ventoux, and Quintana has said outright that he dreams of winning here. Could this be the spot where he finally launches a long-awaited attack and takes the battle to Froome?
3. Cote de Bourg Saint-Andeol
This climb is not the longest, neither the highest, nor the most challenging ascent on this year's Tour parcours. Indeed, on any other stage, it would be a pimple that the peloton crests almost without noticing.
But they won't be in a peloton. The 7km, 409m Cote de Bourg Saint-Andeol comes the morning after the peloton will have climbed Mont Ventoux, at the beginning of the race's first individual time trial on Stage 13. if Ventoux provide the Bastille Day fireworks we expect, the GC contenders could have very tired legs at this point, making the outcome of this TT unpredictable.
If that's not enough, the 37.5km Stage 13 TT also includes a 177m ramp to the finish line at La Caverne du Pont D'Arc to sting the legs even further. This will be far from a simple test against the clock.
4. Col de Berthiand
If there's a theme to this year's Tour de France, it's probably sheer sadism. After a chance to recover on the flat Stage 14, the GC contenders will be warming up on the rollers before the stage yet again as the race hits the Jura.
Coming just 17km into the 160km Stage 15 that will see the peloton climb six categorised climbs - including the snigger-inducing Col de Pisseloup - the Col de Berthiand is a leg-sapping 6km at an average of 8.1 per cent.
It's not the climb itself that could break riders - rather, it's more likely to rob GC hopefuls of energy that could come in very helpful later in the stage when they hit the one-two punch of the next mountain on this list.
5. Grand Colombier/Lacets du Grand Colombier
First included in the 2012 Tour de France, the Grand Colombier is the highest road pass in the Jura and can be approached from mutiple directions.
Stage 15 of the 2016 Tour will see the peloton approach it from two of these - firstly from the north, climbing for 12.8km at 6.8 per cent, then going up an 8.4km, 7.6 per cent grind from the east before dropping into the finish line at Culoz.
The double whammy of these two climbs, accompanied by the previous four categorised climbs on this stage, the travails of the week before and the advent of a rest day afterwards could well see significant changes in the general classification - even if it's likely that a breakaway rider will take the stage like Thomas Voeckler in 2012.