This is the day on which sant eknath left his body in river Godavari and took Jala samadhi at Paithan. Every year in falgun (marathi month) 5 to 6 lacks devotees gather together. Around 600 "Dindi" (mob of warkaries) enjoying three days of this festival. This festival is second largest festival in Maharashatra next to Aashadhi Ekadashi Pandharpur. It takes place around March–April. The 2016 date is March 29.
References
Eknath Sashti Wikipedia(Text) CC BY-SA