If you work in urban planning, design, or development, you understand both the responsibility and the privilege of shaping how future generations experience their communities.

At Citygreen, the part we play is often invisible – hidden beneath roads, pavements, and plazas worldwide – supporting the growth of greener, cooler, more liveable cities.

Our foundational solution is Stratavault: a 100% recycled soil cell system that enables trees to thrive in hardscape urban environments. Manufactured locally in Australia and North America using regional plastic waste, Stratavault supports circular economy principles from the ground up, literally.

Our goal, working in conjunction with you, is to protect both grey and green infrastructure and foster climate positive development of spaces where communities come alive.

circular by design img 1 scaled CitygreenWulugul Walk, Barangaroo, Sydney
20250831 173153 1 2 scaled CitygreenCentral Park, Spruce Grove, Alberta
Starbucks HQ 2019 05 23 G scaled CitygreenStarbucks HQ, Seattle, Washington

When Infrastructure Becomes Art

In 2024, Citygreen was approached by artist and former engineer Mike Hewson and the Art Gallery of New South Wales. Their vision? A 2,000+sqm interactive exhibition (The Key’s Under the Mat) to be constructed almost entirely from salvaged materials, inside a former WWII oil tank.

They needed a structural system that could:

  • check edited Citygreen Support construction equipment, public foot traffic, and playgrounds
  • check edited Citygreen Enable underground services like power and water to be hidden
  • check edited Citygreen Align with a strict reused/recycled materials mandate

And Stratavault ticked every box.

20250805Tank 046 scaled Citygreen
20251003HewsonPreview 107 scaled Citygreen
20251003HewsonPreview 079 scaled Citygreen

Images © Art Gallery of New South Wales. Left – In-progress view of Mike Hewson’s ‘The Key’s Under the Mat’. Middle & right – Installation of Mike Hewson’s ‘The Key’s Under the Mat’, artworks © Mike Hewson.

From Art to Earth: Be Part of the Story

On 4 October 2025, the exhibition opened, built on 3,507 recycled Stratavault modules.

To put that in perspective, that’s around 680m³ of soil vault matrix (enough to support 30-60 trees depending on required soil volume) currently supporting Sydney’s hottest gallery exhibition.

The Key’s Under the Mat is expected to be open to the public until late –2026. with the end of life goal to ensure that as much of the exhibition materials as possible finds a new purpose and home after the exhibition has closed.

In keeping with the spirit of The Key’s Under the Mattheme, we are calling for expressions of interest to determine the next chapter for the Strata-art modules (exhibition Stratavault). Visionary designers, developers, and local governments, – this is a unique opportunity to:

  • check edited Citygreen Secure the world’s most advanced soil cell system (at below market price)
  • check edited Citygreen Embed true circularity into your next streetscape, park, or public realm
  • check edited Citygreen Connect your project to a nationally recognised piece of cultural placemaking

This isn’t just about infrastructure. It’s about legacy, and honouring a cultural collaboration by extending its impact into our streets, parks, and cities.

So, whether you’re planning a small community playground, or a larger project such as civic plaza, green corridor, urban redevelopment or campus transformation, this is your chance to make a unique statement in circular design.

Product quantities and availability: Late 2026 onward

Submit Expression of Interest