Mud Flats
This looked okay from above, but the dried mud was actually only a thin crusty top layer. Upon landing and slowing down to under 5 mph the main wheels crunched through and I nosed over, fortunately without even a scratch to the plane (or me of course). I had to pay however, by pushing the plane back thru the soft stuff to firm ground for take-off, and it was 108 degrees in the shade that day!