Lego was my favorite toy when I was a child and a teenager (I remember still playing with those when I was 17). In fact I still consider it a fun pastime. About a year ago my cousin(13yo) bought a huge Lego set of about 1000 pieces and told me to help him because he couldn't figure it out. I was "off" for about 4h. At first I was just helping him but then I got totally lured in. I was unreachable till all pieces disappeared and the pirate ship was done.
I remember spending long hours playing with my Legos when I was young myself. I didn't have specific Lego set (my collection was a mix of the cheap, little Lego kits) so I couldn't build specific things - I had to use my imagination. So I was building houses or the Hogwart castle (special interest in Harry Potter).
The way I builded stuffs was funny though. At first I was destroying an old building. Then I was separating the pieces by colors and shapes, building one-color towers from them. Then I could finally start building the designed thing. "OK, here goes a blue 1x6 piece... Here it is." - I was commenting to myself.