Any virtual-based science educator should check out the Kitely world, 'Undersea Observatory' for their students. An excellent learning platform. It looks amazing! Undersea Observatory in Kitely Virtual World
OpenSimulator is an open source multi-platform, multi-user 3D application server. It can be used to create a virtual environment (or world) which can be accessed through a variety of clients, on multiple protocols. It also has an optional facility (the Hypergrid) to allow users to visit other OpenSimulator installations across the web from an account on a 'home' OpenSimulator installation.