I don’t usually do direct quotes but this time I couldn’t rephrase it any better. As Wikipedia puts it, “The National Romantic style was a Nordic architectural style that was part of the National Romantic movement during the late 19th and early 20th centuries. It is often considered to be a form of Art Nouveau.”
Helsinki is a mix of many architectural styles, like most cities are, and other styles include neoclassicism, functionalism, and the more ordinary-looking newer buildings that I won’t even bother taking pictures of for my blog. The images here are from the center of town. If you ever visit Helsinki, I recommend you wander around a bit on foot.