Still I didn't had my camera so it's been taken by my old Panasonic.
I did try to think about something natural but all I could find is man-make things.
Here are my photos:
Photo 1:
Blocks
This is not a very sharp rectangle, still, it took me quite a while to photo it so it will be perfectly horizontal.
Photo 2:
Candles
The focus was of course on the light purple candle.
Photo 3:
Milk carton
