'Photoshop'

I was happy with the sketch so I started solving the beast design and working up some values.  I added a few more tentacles around and started to get a feel for the surface and details of the head. As I did this, I kept an eye on the flow of the lines making sure they led to the face which was going to be one of the major focal points. I imagined the body to be a crab-like surface and worked on the arm and claws to get a similar look.      

I did a quick test to see what it would look like if his arm had already hit the ground, but I wasn’t too happy with it. We tend to perceive a lot more tension just before an action happens so I reverted back and worked on the claws to make them more interesting (Fig.03).

Then I started scribbling around the walls to suggest they were covered in hieroglyphs and carvings. The tomb itself had to maintain the theme that something terrible was trapped inside.

The main upper shape is essentially composed of inverted triangles; in psychology of shapes, things that can hurt you like sharp and pointy forms tend to be perceived as evil, as opposed to round and soft ones. Triangles, particularly inverted triangles, are the simplest shapes that oppose round “good” forms, so that was a base for the design. I could have overdone it and put spikes everywhere but I wanted to convey the feel of an old temple made of giant stones, highly decorated, but at the core very rough and functional, in a way similar to ancient Egyptian architecture.
I thought about the façade resembling a stylized octopus head when the portal is closed, those eye-like black holes helped a lot to keep the setting more menacing. The columns on the side re-establish the vertical three-point perspective; they frame the scene and help give the impression that we are looking at something very tall.

The face didn’t look evil enough so I added the horns and there’s a bit of symbolism with the goat-like ears to echo the inverted pentagram and sigil of Baphomet, since it is typically associated with evil (Fig.04).

To get some color I used the texture of a stone wall in Overlay mode on top of the grayscale, making sure the bricks followed my perspective by using the Distort and Perspective transform tools. Then I softened it out by erasing or painting on top. At this point I also reassessed the lighting and worked on the contrast by duplicating the image, putting it in a Multiply layer and erasing out the parts I wanted to stay brighter.

I also turned the hieroglyphs into something more meaningful, using them to add something to the story (Fig.05). I thought it would be cool if the tomb was built in a way that allowed humans to kill Cthulhu and left a hint of it in the carvings. The upper middle section in between the eye-like holes is actually some kind of spear that when activated falls down and is capable of killing Cthulhu.