The ticket can be bought at the entrances to most major sites or at COSITUC (Av. El Sol 103, #102, 9am-5pm Mon.-Fri.). Unfortunately, the pass only lasts 10 days and this is strictly enforced. If you are doing the Inca Trail first, buy the ticket afterwards.
The ticket covers these 16 sites:
If you don’t plan on visiting both Cusco and the Sacred Valley then consider purchasing a lower-priced circuit ticket (US$27). There are three circuits to choose from: the Sacred Valley (over two days), Cusco Inca sites, and Cusco museums (one day only).
Notable sites that are, rather frustratingly, not included in the ticket are the unmissable Coricancha temple (US$3.50) and the interesting Museo de Arte y Monasterio de Santa Catalina (US$2.50), but if you go to both you only pay US$5. The Catedral de Cusco (US$8.50), Iglesia de la Compañía (US$3.50), Iglesia San Blas (US$6), and the Museo de Arte Religioso (US$6) are not covered either, but if you plan to go to all four you can buy the boleto religioso at the entrance of any of these sites for US$17 (US$8.50 for students under age 26 with ISIC card). Other interesting sites not included are the Iglesia de la Merced (US$2.50), Museo Inka (US$4), and the Museo de Arte Precolombino (US$8).
Excerpted from the Second Edition of Moon Machu Picchu.