Gay life in Berlin is starting to echo a darker era.

After the Nazi Party seized power in 1933, Berlin's Institute for Sexual Science was looted, its library burned and staff persecuted. (BPK-BILDAGENTUR)

The fetish cruising bar Bull is a place of pilgrimage in Berlin for more than one reason. To patrons, it is a 24-hour safe space that caters to every palate. To the British historian Brendan Nash, it is a symbol of “Babylon Berlin,”…