rivers and birds could be nice too, as in, just having nature in the bills... but I feel rivers can be complicated to represent in a "unique" way, and birds... meh
@kitten What happened? The Euro Zone isn't anymore about building bridges between countries as it used to be? (that's what bridges represented in the old Euro bank notes)
@kitten Well then you could visit Spijkenisse in the Netherlands. It's open to bicycles. (note the bridge on the bill existed first, it was only ever built because of that)
@kitten True, however it would have been fun if more cities in Europe decided to also build such bridges. The main issue is that just one city in only one country did it...