A Lego mosaic of Seattle I put together for my office. It's 60"x30", which made transporting it here to the office a bit tricky since it wouldn't fit in the car. I overlaid a drawings of the skyline, mountain, and the Space Needle and then converted that into Lego dimensions.
To create a little texture (hard to see in pictures), the white level is one plate high, then the mountain is two plates high, and the Needle and skyline are all a full brick (three plates) high. It's not obvious when you look at it, but I like the slight depth it creates.