If you love comics then Brussels is the city to see them. You will see characters like Tintin, Spirou, Smurfs and so many more. They are all over the city and there is a comic strip route you can take and discover them all. Places I saw them in my trip were buildings, walls, museums, galleries, comic book shops etc.
We actually found the history behind the comics in our walking tour. The tour guide highlighted them and stopped to discuss some of them.
If you do not want to do a walking group tour related to comic books etc...You can discover them on your own or check out all the locations with their visiting Brussels website - https://www.brussels.be/comic-book-route
It's definitely a fun visual way to see this city.
Side Note- Don't forget to buy classic comic books. Ton of book stores sell them throughout the city. read more