blending modes

Seems like iv'e become a bit of a building photographer.
Not really.
I felt bad for not posting forever and looked through my folders to see if i had anything i could play with.
This is a shot i did for one of the companies that helped create this building. They are great clients, like all of mine, so i spent some time taking a few extra shots for them (all of the shots they needed were inside this building).
The photo looked fine without doing anything to it but of course that would be quite boring as i have a perfectly good copy of photoshop on my computer just begging to be used.
To punch it up a bit i went to my channels palate and copied the red channel (just selected all and went to edit - copy).
I then created a new layer and pasted this red channel into it (edit - paste).
I changed the new layers blend mode to multiply and lowered the opacity to 40%. This muted the colors and tones a bit so i went to my background layer and applied a curve where i increased the whites and blacks on the curve, just to pop the contrast a bit.
What this new layer did was to darken the parts of the image that were not red, like the sky and grass.