Find the Culprit File. Solution
Among all the above Answers.. you could simply hit this command on the Terminal to find out the culprit file...
This command finds all the individual files whose size is greater than approximately 100MB and then prints them on the terminal.
sudo find / -type f -size +100000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'
In my case there was a tomcat log file which went to whooping 13GB.