I thought the Representing the First 4,000,000 Decimals of Pi in a Single Image was awesome.
I backed up the URL to TWO-N.com to get an email to suggest a “find next” for the Pi visualization.
There I found forty-five (45) visualizations that you will need to see to appreciate.
Not billable time to a particular client/project.
Some experiences sharpen your talents without being billable time.