Google is expanding its Expeditions program, the company’s effort to bring virtual reality-based field trips to the classroom, with the launch of a dedicated Android application for schools and educators who want to take their students on virtual adventures by way of mobile devices. Additionally, Google says it’s rolling out two more “Expeditions” – that is, the virtual experiences enabled by the program: the Great Barrier Reef and Buckingham Palace.

As you may recall, Google first announced its Expeditions Pioneer Program at its I/O conference last spring. At the time, the company said it would ship out a kit to classrooms that included everything needed to take these virtual trips – like headsets and hardware for the students and the teacher. Specifically, kits included ASUS smartphones and a tablet for the teacher, plus a router to connect all the devices and run the Expeditions app offline, if needed. Google Cardboard or Mattel’s View-Master VR viewers were also provided.

The hardware units began to ship in September in the U.S., and by November, Google said that over 100,000 students had used Expeditions in their classes.

Today, the company says that number has grown to 500,000 worldwide, as the program has since expanded to countries outside the U.S.

Google’s virtual field trips are one of the better use cases for VR technology, as they allow students to experience parts of the world they may never otherwise have the chance to visit – whether that’s the ancient ruins (like those at Machu Picchu), natural wonders like canyons or rainforests, or far-off cities or regions, like Antarctica.

One new Expedition now available, designed and produced by Sir David Attenborough and Alchemy VR, lets students go underwater at Australia’s Great Barrier Reef.

The other, created with the Royal Collection Trust, offers an Expedition of Buckingham Palace. Students can virtually visit the Palace and learn about its historical significance, says Google. (The Palace has also launched its own YouTube 360 video, so anyone with a smartphone can visit virtually, as well.)

The Expeditions Android app, which works on phones and tablets, is today launching into beta and will be made available to select schools and educators who sign up to participate in the program. Participants will also be able to offer feedback about the tours, including what features they would like to see added, and what new places they would like to virtually visit.

Google is offering a sign-up form here for those interested.