This postcard has quite the international connections: A French postcard printed in Switzerland, bearing a message in German, mailed to Austria. There is a crease just left of center at the bottom and some kind of light brown stain (coffee?) across the message area. But still, that date of December 28, 1898 -- oh la la! If you're looking for 'oldest postcard in my collection' bragging rights, this card just might qualify.
Note the publisher of this Souvenir de Paris card was Carl Künzli. My favorite postcard web site, The Metropolitan Postcard Club of New York, says that Carl sold his publishing firm to his uncles a year later, in 1899. All parties concerned had a reputation for producing high quality chromolithographs.
Size: about 5.5 by 3.5 inches. The card is a pale blue-green monochrome. The direct scan shows the color more accurately than the photo.