Pop

 There are a few ways to pop photos. You will find the best one for you. Try the Exposure  slider under colour. Also the shadow & highlights filter. In GMIC there is a special filter to pop shadows, under lights and shadows. Contrast as said will sharpen your photo, as well as making it darker & brighter it also makes the colours more enhanced. I rarely use the saturation filter since I found this out.

Here is a tutorial to make shadows pop

This beginner’s tutorial describes how to make shadows pop in GIMP without that overly cheesy “HDR” look.

1. Open a photo in GIMP. In this example I’m using a plain ol’ JPEG.

2. Duplicate the layer and desaturate it.

3. Invert it.

4. Set blending mode to “Overlay”, strength 50.

5. Duplicate the base layer again, move it to the top and set blending mode to “Lighten only”.
   A side-effect of this lame tone mapping technique is that high radius halos mighty appear, and the sky could be darkened in a cheesy way. You would more easily notice halos in what should be an even blue sky than in grass or rocks. As we only want to make the shadows pop and we don’t want a fake “HDR look” cheesy sky, we fix it in this step. This layer’s job is to undo the effects of this whole technique in the light areas.

6. Go back to the black-and-white layer and blur it. How much you blur it depends on how large your image is and on taste, that’s why I left this step for last. Try 30 and go from there.
   Tutorial by Morgan Hardwood