Reality Media, the immersive book, is realized a suite of Hubs rooms divided into galleries and linked by portals.
This 360° image offers a glimpse into one of the galleries (the Genres gallery).
You can scroll around with your mouse. But you cannot enter this space until you follow a portal in gallery.
Explain that the galleries are grouped into Hubs rooms. These rooms are actually web pages too, being rendered on your browser.
The Hubs Platform
The documentation for Mozilla Hubs is available at in the Hubs user documentation.