it is. The film is called Zardoz. Google at your peril
Zardoz ends in a wordless sequence of images accompanied by the sombre second movement (allegretto) of Beethoven's Seventh Symphony. Zed and Consuella, dressed in matching green suits and having fallen in love, then sit next to each other in the cave-like stone head and age in time-lapse. A baby boy appears, matures and leaves his parents. The couple eventually decompose into skeletons and finally nothing remains in the space but painted hand-prints on the wall and Zed's Webley-Fosbery revolver.
Zardoz ends in a wordless sequence of images accompanied by the sombre second movement (allegretto) of Beethoven's Seventh Symphony. Zed and Consuella, dressed in matching green suits and having fallen in love, then sit next to each other in the cave-like stone head and age in time-lapse. A baby boy appears, matures and leaves his parents. The couple eventually decompose into skeletons and finally nothing remains in the space but painted hand-prints on the wall and Zed's Webley-Fosbery revolver.