Separation and reconciliation. Even official architecture can harbour surprises. The Burg in Graz, official headquarter of the regional government, is a real gem. Centuries of reconstruction have yielded interesting elements of the Gothic, Renaissance and Biedermeier eras. Particularly striking is the double spiral staircase, seeming almost like an optical illusion. This “staircase of reconciliation” consists of two opposing spiral stairs, which merge briefly on each floor, part and then rejoin.
https://www.graztourismus.at/en/see-and-do/sightseeing/sights/burg-double-spiral-staircase_sh-1240