Wiring channel under bathroom floor

[Bill]

I stole this photo from Scott Walters on TMF. Years ago, I needed to run a new wire from the converter (under the tub) to the refrigerator area (under the kitchen counter). How did TM get those wires across the bathroom floor? After a lot of painful probing, I could only figure that TM had "hacked a channel somewhere under the bathroom floor". That description wasn't really helpful to other owners, but it was all I had. Now, as part of a plumbing question, Scott has made it clear. Thanks, Scott.