As commented on the by now closed note: https://www.openstreetmap.org/note/3322846

West to the 3 elevators, there is a staircase leading all the way from 1. OG to 6. UG. (the staircase goes one further down than the elevator. I assume so at least, as the assumend level "6. UG" (=basment) is not accesible to the public. The staircase is located east to the elevators from 4. UG to 6. UG


EG. Viewed from roughly west. Staircase west of elevators.
https://pictshare.net/f203xw.jpg

Staircase and elevators at 5. UG. Viewed from roughly west
https://pictshare.net/stmj92.jpg

Staircase at 5. UG. Staircase east of the elevators
https://pictshare.net/1xqbid.jpg

Staircase switches from west to east on 4. UG (coming down)

elevators at 5. UG
https://pictshare.net/sqbih2.jpg

via StreetComplete 45.2