You can choose to take courses that are not part of your own degree programme. Therefore they do not count towards your diploma. These courses are not in your curriculum and are therefore 'extracurricular'. A minor can also be followed extracurricularly.
You can also apply for the Honours Programme. Through this programme you will follow 30 EC in extracurricular courses. You receive an Honours mentioning on your diploma if you complete the Honours Programme as well as your bachelor's programme within three years, with a grade average of at least 7.5 for your regular bachelor courses.
If you want to include an extracurricular course in your degree programme, go to Submit externally achieved result to see how you can submit a request.