The difference between temperature highs and lows is not much this month: you’ll have highs around 68° F (20° C) and lows around 45° F (7° C). December sees this swathe of the Andes approach its highest rainfall of the year, although there are always breaks in the showers. Generally the pattern in wet season is that the heavy rain comes in the afternoon. Mornings are often still dry.
On the Inca Trail, you may dodge the worst of the rain with more hiking in the morning, but there are many exposed sections of path with no shelter and you are unlikely to totally avoid the showers. The trail also gets pretty muddy, and the risk of landslides is increasing. In any case, all the rain is certainly good news for the flora which is once again flourishing all along the Inca Trail following a few weeks of wet weather.
Crowds & Costs
Crowds are low at the beginning of the month because of all the wet weather but spike again during the last ten days of December because of the Christmas holiday season. Many Peruvians from other parts of the country descend on Cusco and the smaller Sacred Valley towns to visit family and friends.
With good luck and planning, you can still get decent weather on a visit to the region this month and not have to share it with too many other holiday-makers. Bad luck and no planning, and you could be surrounded by bus loads of other tourists in a continual downpour.
Except in the Christmas holiday period, the low season bad weather inclines many hotels and tour companies to offer great deals at this time of year.
Where to Go
Cusco has a lot going on in December, with the Fiesta de Concepción Inmaculada at the beginning of the month and a handicrafts fair and cracking New Year celebrations towards the end. With worse weather often curtailing outdoor activities, it is perhaps a place to spend more days than you would at other times of the year.
Take extreme care if attempting any walk involving precipitous drops such as the exposed sections along the Inca Trail, or the hike up to Wayna Picchu: the rock is very slippery following all the rain.
What to Do
Attending one of December's many festivities is a great idea this month. The weather is worse than usual, and there is more on than in many months. Cusco, as at other times of the year, is the place where most festivities happen.
Persistent rain might make longer, multi-day hikes like the Inca Trail less tempting, but there are a number of amazing day hikes in the region: see here for some of the best day hikes in the Sacred Valley. Remember mornings can still often be dry, even in this rather wet month: start one of these hikes early and you may still get clear skies for the whole walk.
Rafting on one of the stretches of river around Cusco is also generally great right now as rain swells rivers. There are some Class IV rapids hereabouts by the end of the month.
Flora is thriving too. Nature-lovers can expect to see many species of flowers flourishing in December along the Inca Trail, including orchids.
Bear in mind that if you wish to travel by train from Cusco to Machu Picchu (Aguas Calientes train station), services from Cusco's Poroy train station stop operating as of the end of this month: come January, you will be taken by bus from for the Cusco-Ollantaytambo leg and continue by train to Aguas Calientes from there.
Fiesta de Concepción Inmaculada: The feast of the immaculate conception is celebrated on December 8 with processions in honor of the Virgin Mary, particularly in Cusco but also elsewhere in the region.
Handicrafts Fair: The Santuranticuy Fair, taking place on December 24, is among Peru's largest artisan fairs. Held in Cusco Plaza de Armas, its focus is the religious figurines and decorations Peruvians like to decorate their homes with. However it can also be a good source of interesting souvenirs.
Christmas/New Year (Navidad/Año Nuevo): Christmas itself is a religious and low-key affair by Peruvian standards, but New Year celebrations in Cusco are famous across the country. The beautiful city backdrop, illuminated by multiple fireworks, attracts revellers from far and wide.