There are Inca ruins and then there are Inca ruins. Machu Picchu, however, stands apart as the most famed Inca ruins by far. This archaeological site is a national tourist industry in itself. Go to Cusco, and you will end up in Machu Picchu - whether you want to or not.
There's good and bad to be said for that. The good is that the fame is well deserved: The view is breathtaking, the ruins are well preserved, and with a limited number of tourists allowed there each day, the site is taken care of. The bad is that it is an industry: You can buy a packaged trip in Lima, which will set you back around $1000, or you can have at it yourself, in which case you will end up paying around $250 or so. As we will see, however, what you don't pay in money, you pay in pain. If you chose to have at it yourself, you need to get one ticket to enter Machu Picchu (valid that day only); a train ticket to (and back from) Aguas Calientes, a small town at the foot of the mountain upon which Machu Picchu stands and which is only reachable by train; and, unless you want to walk up that mountain, a ticket for the bus that goes from Aguas Calientes to Machu Picchu. Some of these tickets require you to deal with broken websites and travel agents who may or may not be trying to fleece you, and to bring your passport with you at all times, which will be checked again and again. At the end, I half expected someone to say that if I wanted to bring shoes with shoelaces to Machu Picchu, I'd have to buy a special "boleto shoelace-o", only $50, special price for you my friend.
Either way, you will end up at Machu Picchu. There, the sun will either be roasting you in a blistering hot stone furnace, or it will be raining. (I got the rain.)
And it will be fantastic.