Gleis 21 is an innovative co-housing project located in Vienna's Sonnwendviertel district near the Central Station, completed in 2021. This zero-energy building features 34 residential units designed through a participatory process involving future residents, from urban planning to precise details like socket placements.

The project is founded on three core principles: "living in solidarity," "enjoying wisely," and "creating through media." It emphasizes community living while preserving individual privacy. The ground floor is purposefully designed to be open to the public, hosting cultural events, a media workshop, and a bistro, fostering connections with the wider neighborhood.

Constructed as a wood-hybrid building with sustainability at its core, Gleis 21 incorporates numerous shared facilities including a communal kitchen, library, sauna, workshop, fitness room, and laundry areas. All apartments feature private balconies, and the building includes flexible "flex units" reserved for refugees, demonstrating its commitment to social inclusion.

The residents actively participate in the building's management through autonomous working groups, embodying a sociocratic approach to housing. Each resident contributes 10-15 hours of work monthly to the community. The project also collaborates with local media companies and cultural organizations to create a vibrant community hub.

Gleis 21 represents a new model for urban living that balances private and communal spaces while promoting sustainability and social engagement, essentially bringing "the village to the city."