Anyone know how to find a free or unique casino tour in [City Name]?

I'm planning a trip and I've heard that some major casinos offer special, free tours that let you see the back-of-house areas or learn about the history of the venue. I'm specifically looking for something 'unique' rather than just a standard walkthrough. Has anyone here had luck finding a 'gratuit' tour? I checked the official websites but couldn't find any details on booking these. Any tips on contacting the casinos directly or finding a local guide who specializes in this would be greatly appreciated. Thanks in advance!