After Trekking To Machu Picchu
Many guide services include a train ride from Aguas Calientes to Ollantaytambo or all the way to Cuzco as a part of the guided services. In the former situation, trekkers are expected to pay for their own bus from Ollantaytambo to Cuzco and are informed of this in advance. Taking the bus from Ollantaytambo to Cuzco as opposed to the trains full route saves a half hour to an hour. Inquire with your tour operator in advance as to which tickets they purchase. Tickets purchased by the guide services to Ollantaytambo can be changed at the station the day of or the day before depending upon seat availability. Change fees can range from 0-$20 depending upon the class of train that is being changed to. Arrive at least 45 minutes early as there may be a line, for the earliest trains 5:30 am the ticket office opens at 5 am.
Travelers & Trekkers can make excellent use of the obligatory return trip to Cuzco by staying the night in Aguas Calientes after visiting Machu Picchu and visiting the Ollantaytambo ruins, the salt mines near Maras/Urubamba, the Incan agricultural lab of Moray, or the ruins above Pisac the next day all of which are along the route back to Cuzco in that order. Choose two sites and allow a half day for each site for relaxed viewing, transit, and meals. The last buses from Pisac to Cuzco leave around 8 pm. Be aware of your belongings on busses after dark. Or, stay in Pisac and backtrack to any of the sites the next day. Inquire at Ulrike's cafe in Pisac for lodging recommendations open until 9 pm.
By Rail
Two types of trains arrive at the station. The first is locals only that is heavily monitored to ensure no tourists ride it. There are hefty fines if caught on the locals' train. The second is the tourist train which runs Cusco/Ollantaytambo/Aguas Calientes. If you are doing the Inca Trail, you will want to get on the train to Aguas Calientes and get off when the train stops mid-route.
There are three types of tourist trains. Ordered by descending price, they are the Hiram Bingham, Vistadome, and Backpacker trains. Go to Peru Rail's website for the current prices and schedule.
If you purchase a ticket from Cusco to Aguas Calientes, you cannot get off at Ollantaytambo for a few hours and then use the same ticket from Ollantaytambo to Aguas Calientes. If you want to spend time in Ollantaytambo, it is more cost effective to take a bus to Urubamba from Cusco and then a connecting bus to Ollantaytambo or a direct minivan.
By bus
There are frequent buses to and from Urubamba 2 soles; further connection can be made to Cuzco there 3 soles. At 3:50PM, 4:40PM and 5:20PM there are direct buses leaving from Av Grau 525 in Cuzco 5 soles. how much time does this trip take, more specifically? i who ask would guess ~3hrs, up to ~4 if you need to make a change on the way
By Combi
There are combis that travel frequently between the market in Ollantaytambo and the bus station in Urubamba. They are crowded, but at 0.45 soles one way it is by far the cheapest way to travel.There are also comfortable mini-vans which run between Cusco and Ollanta via Urubamba for 10 Soles for the 1 1/2 hour trip. They run all day, leaving when full. In Cusco, catch the vans on Calle Pavitos, which is between Belen and Av Grau, 3 blocks West of Av El Sol.
From Pisac : you will have to make a connection in Urubamba. Pisac-Urubamba in taxi cost 20 soles, or with buses schedules uncertain but much cheaper for 2 soles.