This week, the Seattle city council approved a timeline to tear down the elevated Highway 99 viaduct, a double-layered roadway that was damaged by an earthquake in 2001. As Seattle presses on with its expensive and sometimes controversial plan to bore an underground replacement Highway 99 tunnel, some groups are questioning what will be done with the land underneath the existing highway.

While plans to revitalize Seattle’s waterfront in 2019 have been well-publicized, an opportunity to add more public space to the offering may lurk even further down. The Highway 99 viaduct currently runs over Battery Street Tunnel, a 2,000-foot-long, 60-foot-wide artery under the street, scheduled to be decommissioned alongside the viaduct. Although the Washington State Department of Transportation (WSDOT) plans to fill the 120,000-square-foot tunnel with concrete, Recharge the Battery, a collection of architects, artists and planners, have proposed activating the roadway as a public space.

After Recharge the Battery took public comments in September on how to transform the space, some of the ideas that came to the forefront were an inclusive public park, bath house, interactive art gallery, monster hall of fame, and turning the tunnel into a skate park. The group has argued that, following successful adaptive resuse projects in cities around the world, such as the High Line and Transit Museum in New York, giving the Battery Street Tunnel a second life isn’t impossible.

“To look at the tunnel simply as a liability and fill it in is a one-sided take,” said Jon Kiehnau, Recharge the Battery ‘s co-founder. “You have to look at the fact that the tunnel is 120,000 square feet. Based on the current price of real estate it’s worth more than $100 million. You have to look at what a positive thing it can be.”

Although competing visions for the tunnel have been offered, it’s uncertain whether WSDOT would alter their infill plans, or even decouple the decommissioning of the viaduct from the destruction of the Battery Street Tunnel. WSDOT spokesperson Laura Newborn has stated that the department is legally obligated to fill in the tunnel, as it has become seismically unstable and expensive to maintain. Even Recharge the Battery has acknowledged that retrofitting the tunnel to meet seismic safety standards could cost anywhere from $10 million to $100 million.

With WSDOT scheduled to begin decommissioning work in February, Recharge the Battery and the general public only have a few months left to plead their case.