Holodeck

Star Trek fans will be familiar with the concept of holodecks ... press a button on the wall and your classroom changes into a new environment ... a farm yard, hotel lobby, meeting room, tropical island ... these exist in S.L. and there are several available on the market, to buy.
After some research I decided to buy the model available from HORIZONS ... they have been around for a while, seem stable and also have a professional version that allows you to build you own scenes.
vendor and details at ...
http://slurl.com/secondlife/International%20Schools/40/87/73
You can also buy scenes that other users have made.
The isi holodeck is floating about 100m up in the air above mountain top 2.
Ironically .... immediately after buying this version I found a cheaper one that plugs into the Mysti HUD ... so now have two ... this second one is carried about by my avatar who can throw up a scene at the press of a button ... providing he has building privaleges on the land.