The first thing that caught my eye was the use of minifig legs in the curved wall of the tower. Also notice the 1x2 hinge bricks. If you go to the linked picture, you can also see the great use of half arches.
Here we have a better photo revealing the construction of the curved steps. It seems to be using 1x1 clips attached to a rod which allows the steps to be constructed using SNOTed 1x bricks. EDIT: Marian said this about the construction of said steps: "The curved steps are made from Tile 1 x 1 with Clip on top of Slope Brick 75 2 x 1 x 3 with two 1x3 bricks, attached to Antenna 4H."
More interesting pictures - the techniques are pretty self-explanitory:
Notice the steps in the middle of the photo constructed using 1x4 fence pieces.
Suitcases used for drawers and classic capes for fireplace curtains...
...and more suitcases used for steps!
Check out the table legs!