Tuesday 20 July: Bagnères-de-Luchon to Pau - 199.5km
After two tough days in the saddle, things are only going to get worse here as the first 138km comprises one monstrous ascent after another. The Col de Peyresourde (11km at 7.4% - category 1) is first up after just 11km and the series of steep hairpins towards the summit could splinter the field early before the sharp, kinking descent which follows.
The peloton will then pass over the tricky Col d'Aspin (12.3km at 6.3% - category 1) before pressing on to the big one - the legendary Col du Tourmalet. This 17km rise has an average gradient of 7.4%, the final 12km of which ramp up to merciless 8.2%.
Team Sky's riders will be boosted to learn that many fans have decided to congregate here to cheer their heroes over the 2115m summit. Even when they do that though, they will still have the mighty Col d'Aubisque (29.2km at 4.2% - hors catégorie) standing in their way before a 60km descent into Pau.
Although attacks on the mountains will undoubtedly do damage, organised chasers should be able to limit their losses on the plunge back down into the valley, but this will still be a highly decisive day.
TV Coverage: Live on British Eurosport between 1000-1700* and on Eurosport HD between 1030-1630*. Viewers can also watch live online at www.eurosportplayer.co.uk
*Times subject to change