If anyone speaks Hungarian, perhaps they could translate the name of the site III. katonai felmeres for me. Fortunately, English text on the website explains what you find there: maps from the the 3rd Military Mapping Survey of the Austro-Hungarian empire, covering much of Eastern and Central Europe. The range covered goes from Istanbul in the southeast to Cologne in the northwest:
265 maps are available in JPG format, each about 3-5 MB in size (15-20 megapixels, with varying aspect ratios); you can select a map to view by clicking on the appropriate square on the above map at the site, or select from a list with information about the maps, including their publication dates. 1880-1914 seems to be the date range, with most after 1900, and none post-dating the start of World War I in 1914. A quick look at a few maps show that some of them only have rudimentary terrain shading:
While others have some topographic contour lines (no intervals in this case, though summit heights are given):
Of interest to those who want to see what Europe looked like before the two World Wars.