Edit in JSFiddle

Cesium.TerrainProvider.heightmapTerrainQuality = 0.5;

window.setTimeout(new function() {
  // Add a WMS imagery layer
  var imageryProvider = new Cesium.WebMapServiceImageryProvider({
    url: 'https://services.sentinel-hub.com/ogc/wms/b7b5e3ef-5a40-4e2a-9fd3-75ca2b81cb32',
    layers: '2_COLOR_INFRARED__VEGETATION_',
    minimumLevel: 4,
    maximumLevel: 16,
    parameters: {
      time: '2017-12-19/2017-12-19',
      gain: 0.8,
      transparent: true,
      format: 'image/jpg',
      showLogo: false,
      maxcc: '100'
    },
    tileWidth: 512,
    tileHeight: 512,
    rectangle: Cesium.Rectangle.fromDegrees(1, 41, 3, 43),
    credit: 'Copernicus Sentinel processed by Sentinel Hub [CC BY-SA 3.0 IGO]'
  });

  var terrainProvider = new Cesium.CesiumTerrainProvider({
    url: 'https://assets.agi.com/stk-terrain/v1/tilesets/world/tiles',
    requestWaterMask: true,
    requestVertexNormals: true,
    credit: 'EU-DEM, USGS, Earthstar Geographics SIO'
  });


  var viewer = new Cesium.CesiumWidget('cesiumContainer', {
    imageryProvider: imageryProvider,
    terrainProvider: terrainProvider,
    scene3DOnly: true
  });


  viewer.camera.frustum.fov = 1.7;

  viewer.scene.fog.density = 5e-5;
  viewer.scene.fog.enabled = true;
  viewer.scene.globe.enableLighting = false;
  viewer.camera.lookAt(Cesium.Cartesian3.fromDegrees(2.456645965576172, 42.518991483961145), new Cesium.Cartesian3(1000.0, -4000.0, 5000.0));

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(2.456645965576172, 42.518991483961145, 5000.0),
    duration: 30,
    maximumHeight: 8000,
    orientation: {
      heading: Cesium.Math.toRadians(175.0),
      pitch: Cesium.Math.toRadians(-35.0),
      roll: 0.0
    }
  });

}, 2000);