This is the largest single piece of iron on the surface of the earth (more than 60 tons). It fell about 80,000 years ago in present-day Namibia, and was discovered in 1920 by a farmer plowing his field. The unusual flat shape increased atmospheric drag, and slowed down its terminal velocity so much that it did not leave a crater.
This was unusual because of its flat surface. This made it slow down and hence it only hit earth with a thud rather than a crater creating explosion.