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If you have a smartphone, you can use an app to start learning a new language. One popular and free app is Duolingo.  Many of these programs are set up in a game style to keep you motivated.  If you don't have a smartphone, you can also use a tablet or a computer. Coding is a sought-after skill in many fields, so learning to code is definitely a plus. Many places on the internet offer free coding classes, such as Code Academy or W3 Schools. Some lessons are set up more like a game, while others, such as the W3 Schools are just straight-forward tutorials you read through. Expand your mind by taking free online courses from professors around the world. Many sites are offering courses where you can listen to lectures, engage with other students, and even earn certificates in a wide variety of topics. Try Khan Academy or Coursera to get started. Some universities are offering these types of courses directly through their websites. While you won't get course credit, you can still learn a great deal. One university you can look into is Princeton University.
Work on learning a language. Learn to code. Take free online courses.