Google has set up a way to use Google Hangouts video chatting to set up virtual field trips. Google Connected Classrooms is a way to to connect teachers with organizations that can offer interesting tours and discussions through Hangouts On Air. On Google Connected Classrooms, teachers can find a calendar of past and future Google+ Hangouts.
The teachers can register their classrooms by clicking through the relevant event page on Google+. Some of the organizations that have set up virtual tours already are the Minnesota Zoo, Seattle Aquarium, the American Museum of Natural History, and the Philadelphia Museum of Art.
You can learn more about Google Connected Classrooms at http://connectedclassrooms.withgoogle.com/.