see + do
It really depends on what kind of a visitor you are. If you just want to go and walk around to see the magnitude of Machu Picchu then absolutely, you can go on your own. If you're more interested in the theories on what the buildings were and what life was like before the city was abandoned, then you will want to check into a tour or at least a guide book. I had a tour guide and the tour took around 3 hours. I would have really missed out without the tour and left without the insight that the guide offered. A guide/tour can also provide insight on when to visit, where the best views are, and what else to see in Aguas Caliente as well.