Reading the capitals from the ground directly gives !BRAVKOELLTX..., so there has to be something more to it. The insight here is to become aware of the repetitive structure of the staircase (segments of 11 steps separated by platforms) and the possible positions of the labels (3) and rewrite each flight of stairs as a 11x3 table (as visualized in the pdf). This is also hinted upon by the first flight of stairs (the upper left and lower right corner; the exclamation mark).

The second step is to notice that each element of the table is used only once in the whole set of 17 tables. Therefore, we can combine all tables together and get (read column-wise):

Since one of the hints in the last instructions was to study the Vigenere cipher, it should be clear how to use the key. But how to order the lower case letters? We can observe that the labels on the flight of stairs near the top consistently lack lower case letters, whereas the holes in a similar 11x7 table of small letters are pretty much random. This suggests that the we should use the floor-top ordering and not the table: jcpjrrhrebmexbiqtaauueaxkww. Using the key "rain" (j+r=s,c+a=c,...): SCHWARZENBERGBAD CASH DESK TWO