Grazer Burg

Inside the Grazer Burg, in a courtyard that serves as the entrance to the Styrian state government offices, there is a Gothic (medieval, 12th-15th century) double spiral staircase from 1499 where two independent staircases intertwine without ever intersecting. You can walk up one while another person walks down the other and never cross paths.

The Grazer Burg at Hofgasse 15 contains a freely accessible Gothic double spiral staircase from 1499 where two independent staircases wind around the same central axis without ever meeting. You can climb one while someone else uses the other without crossing paths. The trick is purely geometric: two helixes sharing a center, separated by a continuous wall. The Burg was originally the residence of Habsburg dukes of Inner Austria and is now the seat of the Styrian state government, so the staircase sits in an active administrative courtyard. Free entry during government hours (weekdays approximately 8:00-17:00). Two minutes from Hauptplatz; combine with the Cathedral and Mausoleum of Ferdinand II immediately adjacent.