Vinicunca or Rainbow mountain is a place near the Ausangate. The mountains are are partly formed of colorful sediments, which give the site a unique and surreal look. The mountain itself can only be accessed by foot or horse. From the nearest road, there's a trail leading up, which takes about three hours to walk. Including the three hours drive from Cusco, it takes around six hours in total to reach the top. You can find the trail in Open Streetmap and it's well marked and easy to follow, even if you're not going with a guide. If in doubt, just follow the hordes of tourists.
Although there are a few people living in small villages around the place, it was only discovered for tourism in 2015. The first guided tours were available in January 2016, but by now most of the agencies in Cusco offer one day trips and the place is on its way to a becoming a major tourist a attraction. On popular days (especially weekends) the site can get real crowded, with several hundred people climbing to the top at the same time. Be aware that the lookout itself, from where you geht the best views of the actual Rainbow Mountain and it's surroundings, is just a small hill that fills pretty quickly. All guided tours reach the top at about the same time, so while there's not much people around most of the time, there's a lot around noon. If you want to make sure to get some time for yourself, the only way is going by yourself or spending the night around the area.
Since the region is getting more and more popular, it is especially important not to leave any rubbish (including human waste: there's toilets along the way, so use them). Try to stay on the path and don't walk on the Rainbow Mountain itself (there's some kind of fence around it) to preserve this site for future generations.
As with many of Peru's hiking routes the exact location and directions are difficult to find. Here are the coordinates for Rainbow Mountain:-13.869444, -71.303056
The trailhead is a three hours drive from Cusco, with the last third being a narrow dirt road. There are several ways to get this quite remote place:
The only way of getting up is walking, which takes about three hours. You can also rent a horse from the villagers, which is S./40 one way, S./70 for the return trip. Since the first part is rather flat, people will follow you with horses waiting for you to get tired along the way, so normally you can also rent one if you're already half way up. Be aware that when it gets crowded (especially on weekends), there might not be enough horses for all the people.
The breathtaking landscape, loads of alpacas and some wild vicunas (if you're lucky). There's some small villages, and the people there still live in their traditional way of life, including colorful dresses.
If you have time, there's a lot opportunities of walking around and exploring the area. There's not much vegetation, so you can't really get lost, although bringing a GPS device might be a good idea.
There's not much there, but some of the villagers will sell you some snacks. If you want to stay more than one day, you should definitely bring you own food.
There is a small stream you can use for water, but make sure to purify it before drinking, since there are many horses and alpacas around and their shit is just everywhere. Also be aware that you will find less water the higher you go, so don't rely on it and always carry a sufficient supply. In the village you can buy bottled water and some soft drinks from the villagers.
There's no place to stay yet, but you can find plenty of space for a tent. Make sure to ask the people in the village first, although they might ask for some money (be aware that none of them has a job, so they live mainly from raising alpacas and even a few Soles can make a real difference to them). If you don't want to camp just wait a while, there's gonna be a hostel someday.
Be aware of the high altitude of more than 5000 meters. Make sure to acclimatize sufficiently before the trip. Also the weather can change rapidly (as everywhere in the mountains). While it can get hot at daytime, nights can be freezing cold, snow is not unusual. Also the place is really remote, with the only way of getting up being walking or taking a horse. Especially if you go independently, make sure to bring proper equipment, water and food.
Same as get in, easiest is booking the trip with an agency.