Here is a demo of Eons ICube.

The ICube system is the closest thing to a real Holodeck.

And man does it sound excellent.

From their website:

The EON ICUBE consists of 3, 4 or 6 walls according to the users requirements, and that can be setup in any configuration. Thanks to the rear-projection of the images and the flawless image continuity in the corners, the illusion of a complete sense of presence in the virtual environment is created. On top of that, the system is fully compatible with tracking and input devices. It is built on PC technology whereby several PCs are synchronized together to generate simultaneous images in stereo (stereoscopic visualization) on multiple walls seamlessly.

Using a series of infrared emitters, high-end projectors, and stereoscopic active lightweight shutter glasses and position trackers, the result is complete immersion of the user in a virtual world where objects float in space with high quality graphics challenging the best UNIX platforms.

Another Demo from Vimeo

And the official product page:

ICube Page