The Cave Labyrinth

[XCali]

I tried it with my pen but I wasn't able to reach the same result you did, mine looks dull.

Well looking at yours, it isn't about the linework, you can make very basic and rough lines. The trick on getting that high and low effect going is understanding light and shadow a bit better.

Try something. Add four Colour dots to the image on a different layer. The first a bright'ish colour, not white. The next a bit darker but still a little bright. The third darker by some margin and the last quite dark. (Play around with what four you choose, it is better to keep them at FULL opacity, so make sure you choose the right ones for the area.)

Now playing with JUST those four colours, you paint lines with your 2nd colour, add a few to signify steps down. THEN add the 3rd colour like the steps was casting a shadow.
Then you use the 4th colour, a smaller brush to touch closer to the LINES you drew. This signify the parts that gets the least amount of light.
Lastly, where you see the highest part of the stairs, you touch it with your brightest colour.
As highlights give a protrusion feel that stands out, this will give the sense of height.

Hope that helps. I will see to getting a picture done.