Basic Idea:Much as in a third person shooter game you enter a fieldtrip 'world' and explore it. You can find markers which can be clicked bringing up web materials (related images, videos, multiple choice questions). The environment can be customized by the teacher allowing them to put in instructions, self assessment questions and links 'in world'. This means you can re-use the environment for different levels of students.
The video above gives you a nice taste, I am not convinced by the 'learning fieldwork skills' functionality but the other features it shows are very interesting.
As an aside, Declan De Poar came up with a similar idea for use in Google Earth that I remember him showing me.