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PeruPeruPeru.com(2007年).“Day 19: Machu Picchu / Cusco”.Peru The Grand Tour, 21 Days 20 Nights (travel agency).2007年8月18日閲覧。“[...] hike Huayna Picchu the pyramid-shape mountain above Machu Picchu, walk to the Inca Bridge a secret entrance used by the Inca's army, or toward the Inca Trail to find the historic Sun Gate.”
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MachuPicchuPeru(2006年1月26日).“Machu Picchu”.Machu Picchu 2006.2008年8月18日閲覧。“[Inca Bridge photograph] Inca Bridge - carved into the cliff”
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Dunn, Jerry Camarillo, Jr.(2007年).“Machu Picchu”.How Stuff Works.com, Travel, Destinations.2008年8月18日閲覧。“The famous Inca Bridge is located along an ever-narrowing mountain trail that, at some places, is cut into a sheer cliff. The builders cleverly left a gap in a buttressed section of the trail that they could bridge with two logs. As needed, the logs could be removed to make the road impassable to outsiders.”
