Following the second and final rest day, the Tour de France enters what could the most difficult two-day stretch in race history.

Beginning with Tuesday’s 16th stage and then Wednesday’s 17th stage, the remaining 153 riders will face five hors categorie (above category) climbs, the race’s most difficult.

The race for the overall title is still wide open. Six riders are bunched at the top of the standings, including fifth-place American Christian Vande Velde — and all of the contenders are within 50 seconds of the race lead.

But by the end of the final two stages high into the Alps, the race for the final podium will likely have been determined. Only the final long individual time trial Saturday will remain as part of the overall equation.

In Tuesday’s stage, the field will ride 157 kilometers (97.5 miles) from Cuneo to Jausiers. After a flat opening 30 miles, an asce
nt of more than 11,000 feet awaits in the next 50 miles. The first hors categorie effort is the Col de la Lombarde. It’s a narrow, twisting road that boasts a 7 percent grade through 13 miles.

But it’s the first half of the ascent, with some stretches peaking at 13 percent. It will likely mark the beginning of the end for riders who hope to just make it to Paris on Sunday.

Following a 12-mike descent into the ski resort of Isola 2000, the field faces the second hors categorie effort of the day, a monstrous 26.7-kilometer journey to Cime de la Bonette. The climb has stretches that include more than 10 percent grades, and the climb crests at 9,193 feet, the highest summit in France.

The Tour has never crossed the Col de la Lonbarde nor has a stage ever concluded in the small village Jausiers (popular 1,100). So, literally, Tour history will be made.

The expected few riders who scale the two epic climbs will, of course, reap the benefit, a final steep and expected fast 13-mile downhill stretch to the finish.