Methods Used

Here is the original color photo. For this photo I want to show you how you can use two different conversion methods on the same photo.. I know from past experience that the channel mixer with heavy emphasis on the red channel works great on cloudy skies. I also know that trees require the hue/saturation method. So I'll use both.
Steps in Photoshop:First I'm going to convert the sky using the channel mixer method. I'll select the sky and save the selection because I'll need it again when I convert the ground.

From the menus choose:


The image now looks like this:

Notice how when the channel mixer layer was created it also created the layer mask. This means that the channel mixer layer applies only to the selected part of the image, ie. the sky.
Now I'll convert the ground using the hue/saturation method. Since I'm only going to apply it to the ground I'll need to select it before adding the hue/saturation layers. I do this by reloading the saved selection.
From the menus choose:


This is what the image looks like now.

I want to lighten the midtones to open up the shadow area near the base of the hill. I want to go lighter than I normally would because I'll be darkening the shadows later with an S-curve.
Next I'll add toning the image. I'll use the Warm Midtones action.
Now I'll add the s-curve
The S-curve has increased the contrast of the image. However, the building looks a little faded. I'll fix that by going back to the Levels layer and adjusting the mask, "painting in" the shadows.
This is the final image