Experience this 10 km route near Huayllabamba, Cuzco. It is an easy, but physically challenging route and takes about 5-6 hours round trip. The end point of this hike is Yanacocha (Black Lake in Quechua). When it is windless, the lake is indeed jet black and reflects the mountains beautifully.
You can get to Huayllabamba easily by colectivo from Cusco or Písac. The hike starts fairly easy but then gets quite steep and follows an agricultural valley to a higher elevation and then meanders its way to the lake. The mossy forests are magical, but we often struggled to find the way since there is no indication of the route. You might come across (quite wild and threatening) cows and maybe some baby goats (see last picture :-) ). Overall a demanding hike that shouldn't be underestimated: you gain a lot of height on a small amount of kilometers. The views are worth it though.