Thanks in part to Baron Victor Horta, Brussels was a leading center of the Art Nouveau movement starting in the 1890s and ending just before the Great War.
This private house, open to the public once a month, wasn't a Horta creation but one by the architect and artist Paul Cauchie. The graffiti on the facade is just amazing, and if you're lucky enough to get inside, you'll have the chance to walk through early 1900s Brussels. The house was built in 1905.
There are Art Nouveau buildings scattered all over the city, so if you find yourself in Brussels, take a tour.