For the Level Design course at Full Sail, I developed a fully-functional demo in Unity. If you have Unity Web Player, you can play it right in your browser! Just download the game here, extract the .zip file and launch the “Web” HTML file inside. Here’s an example of what the game looks like.
[This will only run in non-Chrome browsers such as Internet Explorer and Firefox. Hold the right mouse button to look around and the WASD keys to move.]