My first encounter with virtual reality room was in Natural History Museum of Vienna.  Unlike most replicas which were built out of prims, Natural History Museum of Vienna was built out of series of images that were designed and placed in a certain way to create an immersive environment.  
I haven't visited other places with such photo-realistic environment ever since. Last week, my friend Zazen Manbi (Jeffry Corbin - Research associate in Physics and Astronomy at University of Denver) teleported me to a skybox in Sciland. The exterior of the skybox was dull but the interior was breathtaking. The skybox was a holodeck, a virtual reality room. With just a click, I could change the environment of this holodeck into a night city life, jungle, museum, mine, cave, coral reef, royal palace, historic building, and many more.
Holodeck is a room full of realistic pictures but different from just looking at pictures of a place, we can explore, be immersed, and have 360 degrees vision in it. It was a great environment to teach and learn. Imagine the difference between learning about cave in a traditional physical classroom and in a cave environment. I know my students will choose to learn in a virtual cave than having no cave at all in our classroom. The virtual reality environments in a holodeck create a motivating atmosphere and a visual stimulation (which are good for learning) on a dime. We don't need to spend a fortune or be in Star Trek: The Next Generation movie (where the term and concept of holodeck were coined) to be able to enjoy learning and teaching in a holodeck.

A holodeck occupies only a small space. We can change the environment inside a holodeck within seconds. It is perfect for educators who teach in SL under a limited budget. (like 
Holodecks are available for sale in Marketplace. There are some freebies too. My friend Aedann Slade, (the headmaster of North Carolina Web-Based Immersive Environment for Education ) gave me some virtual reality holodecks yesterday. I was not able to set them yet but I am determined to learn more about it.

"To teach is to learn"