Alright kiddo, so back in a time called the Belle Époque, which means "beautiful era" in French, there was a lot of really fancy and beautiful architecture in Paris. This was a time when people were really interested in art, fashion, and fancy things, like big buildings with lots of decorations on them.
Many buildings from this time had what we call "Art Nouveau" style. This means they had really pretty and flowy designs with lots of curves and shapes that look like they're from nature, like flowers and leaves. Some buildings had fancy balconies and intricate details all over them. These buildings were made by very important architects who wanted to make Paris look really special and unique.
One example of a Belle Époque building is the Grand Palais. It's a huge building with glass windows and a big dome on top. Lots of people went there to see art exhibits or attend fancy events. Another example is the Moulin Rouge, which is a famous dance hall with a big red windmill on the roof. Some other buildings were made to look like big department stores, with lots of windows and small balconies sticking out.
Overall, the architecture of the Belle Époque was very special and fancy. It was a time when people wanted to show off their wealth and good taste, and buildings were a big part of that. Today, many of these buildings still stand in Paris and you can go and see them for yourself!