Placemark->getElement() returns Placemark

I've got a set of KML files like the attached, and I'm trying to get the value of Placemark->MultiGeometry->LineString->coordinates, but when I call Placemark->getElement(), no matter what value I feed in, it's returning Placemark. What am I doing wrong here?

SWK_Trails_Website.kml

$parser     = Parser::fromFile("path/to/file.kml");
$kml        = $parser->getKml();
$document   = $kml->getDocument();
$folders    = $document->getFolders();
$placemarks = $folders[0]->getPlacemarks();

foreach ($placemarks as $placemark) {
    echo "<pre>";
    print_r($placemark->getElement("MultiGeometry"));
    echo "</pre>";
}