We taped and numbered pieces of cardstock to the floor with painters tape as we designed our mini golf course around the house. We also put a numbered X where each part of the course started.
It was so much fun!
We played a few rounds and B used tally marks to keep score (always sneaking in a little learning).
If you don't want to make your own tunnels like we did, you can use different toys and items for obstacles to hit the ball through and around. We had our tunnel as the last obstacle of our course.