From the intro piece, with emphasised links, on Microsoft's site:
Tucked away on Microsoft’s vast campus in Redmond, Washington, is Building 87, a nondescript building that houses some extraordinary hardware labs.
Now you can take a virtual tour of Building 87 and see where experts created some of your favorite devices.
Control this interactive experience by clicking and dragging with your mouse or using the arrow keys on your keyboard. On your Lumia, simply tap and swipe to explore!
Starting in the B87 Lobby, you can explore three areas: Edison Labs, the lab of the future where the Surface and its Touch Cover were engineered; the Human Factors Group, the place where HoloLens, the Xbox controller, and Microsoft Band were optimized for human biomechanics; and the Anechoic Chamber, a super-quiet sound facility where Cortana and Surface’s speakers and microphone were developed.
Along the way, you’ll learn facts about each lab and its team members as well as see informative behind-the-scenes videos explaining the technical know-how that happens behind B87’s walls.
Go here to start your tour now.
Of course, everything here is carefully curated, it's not as if you can poke around in VR and spot something 'unreleased'! But still a fascinating glimpse. Check it out.