Learn any foreign language! It can open up so many doors to you and offer you a life you didn't think was possible.
During the pandemic I started learning Spanish. After a year and a half of self-study, I went to Mexico City for a couple of months in order to practice. I had such an amazing time that I decided I wanted to spend more time in Latin America, and so I traveled to a few more cities over the course of half a year.
I've met such incredible people, have had amazing experiences, and, most importantly, my mind has been opened to many different ways of being and living. Being aware of those different ways allows you to be more conscious and intentional about how you choose to be and live, which, in my view, equates to more freedom, happiness, and fulfillment.