Complex sentence: It runs for 13 miles and begins at Hillview Reservoir in Yonkers, New York, extending across Central Park to Fifth Avenue and 78th Street and then stretches eastward under the East River and Roosevelt Island into Astoria, Queens.
Split into simpler sentences: It runs for 13 miles and begins at Hillview Reservoir in Yonkers, New York. It extends across Central Park until about Fifth Avenue and 78th Street and stretches eastward under the East River and Roosevelt Island into Astoria, Queens.