 = null;
      let scene = new Scene();
      scene.addNode(new Gltf2Node({url: 'media/gltf/cave/cave.gltf'}));
      scene.addNode(new SkyboxNode({url: 'media/textures/eilenriede-park-2k.png'}));
      scene.standingStats(true);

      function initXR() {
        xrButton = new WebXRButton({
          onRequestSession: onRequestSession,
          onEndSession: onEndSession
        });
        document.querySelector('header').appendChild(xrButton.domElement);

        if (navigator.xr) {
          navigator