Using Google Maps, users can now see indoors.
Here is an example of a Google Business Tour:

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From what we can tell, business owners cannot upload their own tours, but rather, must engage a Trusted Photographer.

This is a shame because it would be cool if users could upload their own 360° Panos to Google Maps. Maybe Google could provide a way to filter out user-submitted content, if the viewer prefers less "professional" tours be excluded?....

While the user-submitted 360° pano tours would not be as interactive as the Professional "walkable" version, it would be a great way for Google to begin to build more indoor content.

It'd also be an awesome way to keep The CRE Map Wars raging...