Pictures. Im unsure about the 3 laters of wall and if i can just open and patch them

From basement

I've a strong preference to not use ducts (supply or return) so I'd likely just open up the walls where necessary to fish the cable down properly.

When I have done that I've used a string (mason's line) or chain w/ a weight on it as my first attempt. Often w/ things like you're encountering you need to bob it up and down, swing it or whatever to get it to go by the obstruction. I've also pushed the weight down w/ a fish stick for better control and then when it get's by the obstruction it will drop on its own. Last option is a fish tape and sometimes again w/ a weight on it.

If these are two different ducts then you'll need to carefully exit at the bottom of the upper run, go through obstructions, and then reenter at the top of the lower run.

- Make sure to ALWAYS seal up each cable entry/exit very very well.

- Plenum approved cable is always a good idea for this type of run but definitely if using a supply duct.

- When drilling through between floors be very careful that you don't weaken anything structural.

- These can sometimes (or often?) result in noise from cable slap caused by airflow slapping the cable against the duct. Besides the noise it can weaken the cable.

I wouldn't put it in a supply duct but Plenum-Rated Cat 5e or Cat 6 in a return should be fine.

Follow opaone's recommendations (above) also

I wouldn't put it in a duct of any kind. I can't imagine that would be code compliant but I don't know for sure.

Putting the cable through a cold air return is perfectly acceptable in the code but not the supply side. The only thing you can't run through a cold air return is gas.

Hmm. Not sure about supply vs return, but this column in fed by the large vent in the second floor ceiling where large foil ducting transtions into the column as shown in the attic picture.

Hence return i believe.

Ideally id love to in once of the two lol outter cavities, the problem being i have no way to know how enter either of those given the view from the attic.

Then im assuming that this 3 layer cavity continues on the 1st floor..

But again, id much rather open holes from the basement and pull down, but from the basement or attic it all looks like one cavity not 3.