Babylon.js/Playground/scripts/collisions.js

var createScene = function () {
    var scene = new BABYLON.Scene(engine);

    // Lights
    var light0 = new BABYLON.DirectionalLight("Omni", new BABYLON.Vector3(-2, -5, 2), scene);
    var light1 = new BABYLON.PointLight("Omni", new BABYLON.Vector3(2, -5, -2), scene);

    // Need a free camera for collisions
    var camera = new BABYLON.FreeCamera("FreeCamera", new BABYLON.Vector3(0, -8, -20), scene);
    camera.attachControl(canvas, true);

    //Ground
    var ground = BABYLON.Mesh.CreatePlane("ground", 20.0, scene);
    ground.material = new BABYLON.StandardMaterial("groundMat", scene);
    ground.material.diffuseColor = new BABYLON.Color3(1, 1, 1);
    ground.material.backFaceCulling = false;
    ground.position = new BABYLON.Vector3(5, -10, -15);
    ground.rotation = new BABYLON.Vector3(Math.PI / 2, 0, 0);

    //Simple crate
    var box = new BABYLON.Mesh.CreateBox("crate", 2, scene);
    box.material = new BABYLON.StandardMaterial("Mat", scene);
    box.material.diffuseTexture = new BABYLON.Texture("textures/crate.png", scene);
    box.material.diffuseTexture.hasAlpha = true;
    box.position = new BABYLON.Vector3(5, -9, -10);

    //Set gravity for the scene (G force like, on Y-axis)
    scene.gravity = new BABYLON.Vector3(0, -0.9, 0);

    // Enable Collisions
    scene.collisionsEnabled = true;

    //Then apply collisions and gravity to the active camera
    camera.checkCollisions = true;
    camera.applyGravity = true;

    //Set the ellipsoid around the camera (e.g. your player's size)
    camera.ellipsoid = new BABYLON.Vector3(1, 1, 1);

    //finally, say which mesh will be collisionable
    ground.checkCollisions = true;
    box.checkCollisions = true;

    return scene;
}