$20 experience?!

My 9yr son came to me with the question of what experience could he have in Auckland for $20 dollars or less?

So far my suggestions haven't cut it. Rather than buy $20 of lollies how would a 9 y/o who's open to most things spend $20 in Auckland on an experience obviously with this budget it's going to be limited but I'm curious to see how creative you all are ! ☺️

Thanks in advance