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Photo: EdsonFuentesMera, CC BY-SA 4.0 via Wikimedia Commons
Ruins of largely religious significance, they doubled as the last and largest defensive structures near the plains below where the Incas defeated the Spaniards in battle. Admission with boleto turistico (can be purchased at entrance to ruins, S/130 for 10 days) or S/70 for "boleto turistico parcial" for a 2-day pass to this and other Sacred Valley sites. Local guides can be hired in the market area below the ruins (S/20-100). Or, do it yourself by purchasing the book most of the guides use, ¨Cusco and the sacred valley of the Incas¨(Salazar and Salazar) which has an extensive section on Ollantaytambo. The book can be purchased in the market below the ruins (S/50) or in advance in Cusco (S/35). Neither the guides nor the guidebook discuss the battles, for information on this research on your own in advance. Tours focus largely on the unique architectural significance of the sun's rays on the cad face of the canyon wall and on the temple walls, the still functioning fountains, and the large stone operating table. Even if you're not an archeology buff or ruins fan, these are worth seeing. Beautiful views abound.
Even if you have not acclimated to the high altitude, the hike (there are steps) to the top of the ruins is doable in 15 min or so. The last segment of the path are one-way – up hill and downhill. From the top there is a lateral trail that can also be taken that will stop by a small granary and then to a path that leads down to ground level. This would probably take another 25 min.
The mountains opposite the ruins have ancient granaries and it's possible to trek up to them as well.
© OpenStreetMap contributors
The hill with Incan storehouses overlooking the town and facing the main ruins. To get to the path up to these ruins, follow the road closest to the base of the hill, Lari Calle (the rightmost one in the town grid when facing Pinkullyuna). You will see a small sign with an arrow pointing to a steep path, which takes you up to a series of ruins and storehouses. Admission is free, and from here you can see some of the most spectacular views of the Ollantaytambo ruins and town and the Urubamba Valley. It's a lovely hike, and can be done in just an hour or two. Some parts of the various path can be a little harrowing, especially the less oft used side paths (all of these also lead to ruins that are less apparent). Go with a friend or at least make sure you let your hosts at the hostel know where you have gone in case something should happen.