Editor’s Note: “ My Happy Place ,” a CNN Original Series following celebrities on deeply personal journeys, airs Sundays at 10 p.m. ET/PT. CNN also tapped its anchors and correspondents to share their happy places. LA’s Griffith Park, on horseback, gives CNN’s Sara Sidner a happy giddy-up. Los Angeles CNN  —  Griffith Park is a massive, mountainous, wild oasis in the middle of the dense urban sprawl characterizing much of this fabled city. Yet its identity is still very LA — fun, sunny and it’s