Why do waffles have bumps?
The bumps are put on the waffle to provide additional surface area, so that the waffle can crisp up and be brown all over in a shorter period of time. Without the bumps, the insides may be under cooked or the surface burned trying to get it cooked all the way through. It also provides a great place for the butter, syrup and/or fruit to collect.
Everywhere in Brussels you can buy waffles. They're called Gaufres Bruxelloises, which stands for Brussels' waffles. Another city in Belgium called Liège, is also famous for it's delicious waffles. They're called Gaufres Liègois, which stands for Liège's waffles. The difference between B waffles and L waffles is that the Brussels' waffles are much more crispier and less sweet. The Liège's waffles are soft and sugared.