If they are asking for "extra-curricular and leisure activities," they are probably more interested in your hobbies/interests completely outside of academics and professional life. If you have a few hundred words to "describe" it, I'd treat it as an invitation to talk about your personal interests, like music, sports, or art, and any clubs or societies you joined at school and why you enjoyed them. So I probably wouldn't mention any vacation schemes or anything work experience-related, because they probably ask this to get a sense of your personality and who you are outside of your qualifications.
If you want to include your past vacation schemes somewhere, you probably can include it in a competency-based question if you're sure it really fits - but I would be sure to make sure your answer focuses on your skills and fully answers the question.