A reference to Bram Stoker's Dracula, which was published in England in 1897.
The Mediterranean is linked to the Black Sea by the Sea of Marmara in Turkey (or the Ottoman Empire, as it then was).
From the port of Varna (bottom right of map) in Bulgaria, they travel northwest to Transylvania, a mountainous region long associated with vampires. Bran Castle (pictured) is thought to have been an occasional home to Vlad Tepes, the original Dracula. At the time, Transylvania was part of the Austro-Hungarian Empire, so it is not surprising Louis finds German speakers. Transylvania is now part of Romania.