Final answer:
Otto Wagner developed architectural projects for Vienna's Ringstraße in the 1860s, including iconic buildings like the Vienna State Opera and the Austrian Parliament Building.
Step-by-step explanation:
The architectural projects related to Vienna's Ringstraße were developed by Otto Wagner in the 1860s. This urban planning project aimed to transform the city and create a boulevard around the inner city.
Wagner's designs included various buildings and structures along the Ringstraße, such as the Vienna State Opera, the Austrian Parliament Building, and the Vienna City Hall.