A while back I had come across a novel method for increasing local contrast and details in an image by German artist/photoshop guru Calvin Hollywood. He called it "Freaky Details", and it basically consisted of an inverted duplicate of the base image that was "Surface Blurred", and had the blend mode set to "Vivid Light".
Unfortunately at the time, I didn't have access to a "Vivid Light" blend mode in GIMP, and wasn't sure how "Surface Blur" worked in Photoshop.
Turns out, though, that "Vivid Light" is just Color Dodge & Color Burn, masked for high and low values against the base image, and that "Surface Blur" was just a bilateral blur.
I asked the G'MIC guys if they could easily add a "Vivid Light" blend mode for me, and they did! So now there's a workflow for replicating this effect in GIMP!
My full tutorial is here:
Also, after seeing the tutorial, the actual filter effect has now been included into G'MIC directly!
Here's a look at a sample result from this: