Be aware that you can only enter Machu Picchu with a pre-purchased ticket, and that you must provide a passport for both purchase and admission. The entrance fee to the ruins is 126 PEN, which equals roughly 47 USD. You must pay in soles. If you're staying in Cusco, then you can buy a ticket from the National Cultural Institute (INC) off of the main square. Once you arrive in Aguas Calientes, you can also buy a ticket at the Machu Picchu Cultural Center near the central plaza. The ticket counter in Aguas Calientes is open from 5.15AM to 7PM. For an additional $12, you can buy tickets to and from the park entrance gate. This can be a great option if you want to avoid an hour-plus walk up to the ruins.