The "marc'al-bahreyn" - literally the "confluence of two seas", is the name given to the place where Mevlana is thought to have met Semseddin of Tabriz for the first time. In time it became a place of pilgrimage for members of the Mevlevi order. The site is now known as Babalik Street, opposite the municipality, before the old Sekerfurus Han.
Above text and pictures are from the book titled "Mevlana and the Mevlana Museum".
You can purchase "Mevlana and the Mevlana Museum" book and other Turkey related books from Explore Turkey Bookstore.