Salineras is a cultural site in the Sacred Valley of the Incas. Admission is S/ 10 (jan 2017). If you come by cab, it will stop at a gatehouse and you have to pay there. You will receive a ticket with a nice picture of the site.
Salt has been harvested from the briny waters of the Salineras spring for thousands of years. There are thousands of salt pans nestled in a canyon, which are used to evaporate water to extract the salt. The salty water is directed to the ponds by an intricate network of channels. Once the pond is filled, the flow of water is cut and it is allowed to dry. Salt precipitates in crystals, and when dry it can be harvested. The salt pan is run on a cooperative system.
To get to Salineras, you have to hike down into the canyon from Maras or up from the road connecting Urubamba to Ollantaytambo. From Maras, walk towards the edge of the valley. Where the road bends to enter the town, there is a path. If you have trouble finding it, ask a local. From Maras it's about a 2 Km hike to the site. The path is very easy to follow. From the Maras turnoff on the Cuzco-Urubamba road you can also easily walk. Go towards Maras for ca. 500 meters, then tske the clear path through the fields to your right. This path meets the main road into the Salineras.
You can continue straight through the Salineras (keep to the left side) down to the rio Urubamba, following a path on the left side of the canyon. Walk through the small settlement on the riverbank and go right to find the bridge. Across the bridge you're back on the main road where you can catch a bus.
To get to the site from the road between Urubamba and Ollantaytambo, stop by Punta Arco de Iris (Rainbow Bridge). If you let the taxi/ collectivo driver know where you are going you should be able to get picked up. It is very easy to get picked up by some form of transportation from that bridge, so it is entirely feasible to start at Maras and end up getting a ride back to your destination down in the valley.
Salineras consists of thousands of salt collection pans, all being filled, dried, and harvested on a rotating basis. They have been in use for thousands of years, and are still being worked today in the traditional manner. They are not worked on Sundays, so plan accordingly. On one hand it is interesting to be able to see the pans being mined by people in traditional garb, but if you go on an off day you are likely to have the whole place to yourself, and can wander around at your own discretion. Moray is in the area and can easily be seen in the same day.