Simple indoor or outdoor putting drill you can do to challenge yourself

This game is called 15. The idea is to make 9 putts in a row. Those putts are from these distances:

• Make 5 putts from 3 feet in a row. 5x3=15
• Make 3 putts from 5 feet in a row. 3x5=15
• Make 1 putt from 15 feet

There are several variations you can add to the game. 

• Don't hit every putt on the same line: Switch the line of every putt, to more of an around the world style. 
• Alternate between distances: Don't stay at the same distance to make all of the putts. Switching your distance, as well as your line is more like real golf. You never hit multiple putts in a row in from the same line on the golf course. This practice make it seem more like real golf. 
• See how many tries it takes you to make 9 putts in a row: This is a challenge drill. A completion drill. Something that you can walk away from the course and feel good about what you accomplished. 
• Take your time: Rushing never helped anything when you are trying to improve. Go through your routine, simulate being on the golf course.

I created a quick video on YouTube to show you how I set this up indoors.