Only a few steps if you're using Photoshop.
- create a duplicate layer of the background (in case you mess things up)
- create a B&W layer - I moved the red slider slightly to the left and the cyan slider slightly to the right (not too much because we'll pick that up in step 4)
- create a curves layer and set to medium contrast
- Now go back to that duplicate background layer and use the dodge and burn tools to add further areas of light and shadow. I lifted the tones in his face slightly with the dodge tool on midtones, then using the burn tool and varying opacity set to shadows I added more contrast and texture to his beard, shirt and stonework.
- Finally I stuck in a vignette because I'd lost all tone from the sky.
You can always tweak the opacity of any of the layers to tone down the effect if it's too much or even reduce the B&W layer to let some colour tint back through.