A simulated sky can be added to a scene using a skybox. This is created using a large standard box, special reflective textures and a group of six images, one for each face of the cube.
Six jpeg images are necessary to create a skybox, all of them should be square and of the same size which is best as a power of 2, eg 1024px x 1024px. The name for each image should have a common part followed by a position given by _px, _nx, _py, _ny, _pz or _nz corresponding whether it is on the positive (p) or negative (n) x, y or z axis.
Example Images
Notice that the images match seamlessly at the edges of the box.
Skybox images can be found on the web by searching for skybox images. Generally these are single images in the form of a net of a box and you will need to seperate them into individual images and save each.
Within the playground you can copy and paste the following into your scene.
var skybox = BABYLON.MeshBuilder.CreateBox("skyBox", {size:1000.0}, scene);
var skyboxMaterial = new BABYLON.StandardMaterial("skyBox", scene);
skyboxMaterial.backFaceCulling = false;
skyboxMaterial.reflectionTexture = new BABYLON.CubeTexture("textures/skybox", scene);
skyboxMaterial.reflectionTexture.coordinatesMode = BABYLON.Texture.SKYBOX_MODE;
skyboxMaterial.diffuseColor = new BABYLON.Color3(0, 0, 0);
skyboxMaterial.specularColor = new BABYLON.Color3(0, 0, 0);
skybox.material = skyboxMaterial;
More generally the the images are referenced in the following way
skyboxMaterial.reflectionTexture = new BABYLON.CubeTexture("PATH TO IMAGES FOLDER/COMMON PART OF NAMES", scene);
Playground Example of a Skybox -