my denoising attempts don't give results as smoothass as the video above. It seems more like a blur filter to me, not post rendering noise reduction through data gathered from rendering.
But I modeled some more 3D locations, here is some WIP...
This Scene is supposed to be a huge balcony made from marble with stairs leading up to it. It is actually just a background, and I want to play some animations in front of it. Also I recorded some greenscreen footage of a friend acting that is supposed to interact with the animation. But for now let's focus on the background

Chosing the correct tiles for the floor is important





After fiddeling around for some hours in the nodes editor I settled for the version you see in the last image. All these little bumps make it so different every time and I could have spent more and more time in the nodes editor just for the floor, but modeling is also fun!

These damned pillars won't stand up straight, not even viagra helps. So screw them standing up, this looks pretty cool this way!

Put a handrail on it and finally throw in some more interesting light than just plain white light. This lights up the bright marble like texture pretty well.

Some more lights with an interesting texture on the surfaces and cool shadows on the upper floor.

I smoothed the surface and made it some rough polished marble... hopefully...

Then I did cut some windows out of the wall and even out of the ceiling. please note the nice light that comes through the ceiling holes onto the main floor


And then the nice ceiling light is not that visible any more when you want to have a spotlight on the action supposed to happen in the foreground.