The Flat Rock Dam spans the Schuylkill River near the Northwest corner of Philadelphia.  It is part of the now long defunct  Schuylkill Canal, first opened in 1828. 

The antenna towers on Ivy Ridge have been a feature of the Philly skyline since the 1950s.  Their bases are several hundred feet above the river but the river bank trees hide the hillside in this view.  To capture their delicate detail I shot this panorama at high resolution, 1.0 gigapixels.