Here is a great example of Art Nouveau (French for 'New Art') used in Interior Design. What you're looking at is a fireplace surround that is capturing the true essence of nature itself. The beautiful ceramic glass uses colors that are found outdoors. Unlike most fireplaces that are characterized by harsh 90 degree angles, this surround only uses soft curves -- just like you'd find in a natural environment. Personally, I find it amazing that an artist can take a hard material, like ceramic, and imbue it with such flowing lines, reminding us of waves -- the tide coming in. Most importantly, the focal point is a mask representing humanity.  Art Nouveau celebrates the relationship between humanity and her environment.
This style is best used in rooms that are meant to make us feel welcome.  Although this piece looks harsh standing on a bare wall, it would be right at home in an Bohemian hotel with young Parisians sitting nearby arguing passionately, wine glasses in hand. Perhaps a beautiful accent to this grand surround could be a classic candelabra (Beauty and the Beast style) with a piece of art by Gustav Klimt --perfect for above the mantle. If this is the taste you desire, then Art Nouveau is exactly what you're looking for!

Attributed to: Desire Muller( French, 1877-1952) French Luneville, ca.1900 Glazed Stoneware