Find a book.
Start that course from Udemy you purchased six months ago.
Learn a new skill.
Run a little farther.
No one is saying you need to master the subject, no one is saying you need to become an expert or invest 4 hours a day.
Catch up on that seminar you might have missed.
Most of all, Summer Learning should be about things you want to learn, not stuff that other people want you to learn, that’s why it’s way easier to do, and more enjoyable.
And that’s what the summer is for.