I used to drive a truck on a beach cleaning crew.<p>We were driving along at about 3 in the morning when the truck suddenly stopped. The wheels were in quicksand. The front of the truck eventually sank up to the headlights.<p>There was a buried outflow pipe from street sewer drains that emptied into the ocean.
The pipe broke and the water/sand mixture turned into quicksand at that point. On a beach at 3 in the morning this wasn't the least bit obvious.<p>Needless to say, the boss was not amused.