Charlotte Ritter and Gereon Rath meet each other when stepping out of an paternoster lift/elevator. A paternoster lift consists of a chain of open compartments that move slowly and constantly in a loop. Their construction--due to safety concerns in many countries--is not allowed anymore. In 1929 they were prevalent, and a common alternative to a staircase. Very few of these elevators have survived due to safety concerns.
When Gereon Rath and Bruno Wolter talk about World War I, Gereon tells him that he fought at the "Siegfried Linie" (Siegfried Line). This was a German defensive position built during the winter of 1916-1917 on the Western Front from Arras to Laffaux.
At Moka Efti, Svetlana Sorokina plays a theremin, an early electronic musical instrument with pitch and volume antennae that sense the proximity of the player's hands; the musician does not actually touch the instrument to play. Introduced in the Soviet Union in 1920, the instrument became a popular novelty in Western Europe and the Americas by the late 1920s, and is perhaps best known for lending its eerie gliding tones to the soundtracks of classic Hollywood horror movies. The theremin later waned in popularity with the emergence of more tonally flexible electronic organs and synthesizers that are much easier for musicians trained on traditional instruments to play.