Adventure Specialists (U.S. tel. 719/783-2076, www.adventurespecialists.org , prices vary, call ahead) leads highly recommended, custom horse-packing trips all over Peru and especially in the Cusco  area. Founder and co-owner Gary Ziegler is a true adventurer, archaeologist, and noted Inca expert.
Manu Expeditions (Pardo 895, tel. 084/22-6671, www.manu  expeditions.com, prices vary, call ahead) offers a range of horse-riding expeditions that explore areas of the Vilcabamba and Choquequirao (17 days), as well as Machu Picchu  and the surrounding cloud forest (15 days). Another of its itineraries is from the Andes to the Amazon (14 days). One- and two-day rides around Cusco are also offered.
The best options for riding Peruvian paso horses is Wayra (part of the Sol y Luna Hotel outside Urubamba, tel. 084/20-1620, info [at] wayrasacredvalley [dot] com, www.wayrasacredvalley.com , US$195 per day) and Perol Chico (Carretera Urubamba–Ollantaytambo, tel. 084/974-79-8890, www.perolchico.com , prices vary, call ahead).