This is a step by step instruction with pictures to create a very simple windmill out of fairly common Lego pieces. Here we go!

Step 1: Step 1

Gather 5 of the "4x4" Lego blocks and assemble them in a straight, vertical tower assembly. You can decide what color blocks you want, or mix and match the colors for more "flare". I just decided to do mine in all green pieces.

Step 2: Step 2

Next, grab a "2x4" Lego piece of any color(I chose white) and then attach it to the bottom of the tower in the center. Leaving just 1 row of the bumps hanging out. It is hard to explain so refer to the picture for details.

Step 3: Step 3

Next, it is time to create a stable base for the structure. Find 2 of the "1x4" Lego pieces and assemble them perpendicular to the piece we just installed in step 2. Refer to the picture for the positioning. Now we have a stable base for our windmill.

Step 4: Step 4

Now, it is time to install the Lego piece that will allow the windmill rotors to spin. It is a little white piece that you will need to refer to the picture to find. It stands out from every other Lego piece so it will be fairly easy to locate. In my picture, it is the little piece at the very top of the structure.

Step 5: Step 5

You're almost done! We are now on the last step to create this little windmill out of Legos.

Find the propeller in our Lego pieces. It will be very easy to find since it looks like a rotor and is fairly larger than all the other regular Lego pieces. Then all you need to do is snap it to the little shaft piece we installed in step 4.

After you've done that, now you're done! Sit back and enjoy your little windmill and now you're able to add it to a little town built out of Legos.