During the nine days of Dashain, people take holy bath in nine divine places. This tradition is called Nava rath. People go to various river confluences early in the mornings to take bath and visit sacred temples and shrines during afternoons.
The following river confluences around Kathmandu valley are considered to be holy river for Nava Rath bath for the nine days of Dashain. The bath is taken from Ghatasthapana to Navami. Accordingly, the temples near the conflunces are worshiped on the same day.
Nine forms of Devi Durga is worshiped during Dashain. Devis are symbols of different divine powers in the form of Goddess Durga. In other words, these are manifestation of powers of Devi in various forms.
Durga is worshiped in eight form also. These forms are called Astha Matrika or eight mother divine.
Sources includes :http://www.nepalhomepage.com/society/dashain/main.html