Parcel 12 on Boston's Rose Kennedy Greenway is shown with temporary shipping container-based art galleries. Photo courtesy of The Rose Kennedy Greenway Conservancy.

The nonprofit that manages downtown Boston’s Rose Kennedy Greenway wants ideas for how to make the only remaining undeveloped parcel over the Tip O’Neil Tunnel more lively.

The Rose Kennedy Greenway Conservancy issued an request for expressions of interest yesterday for Parcel 12, a grass-covered lot opposite the Dock Square Garage, slated to be expanded with a 6-story, 243,500-square-foot addition containing 209 luxury condominiums.

The RFEI ask for ideas for how to improve the 8,500-square-foot crescent-shaped portion of the site. In the past, Parcel 12 has been home to temporary zip lines, shipping container art galleries and public outdoor art pieces.

“This RFEI is seeking submissions that are creative, innovative, and park-appropriate,” the document states. “We are open to new, big-picture, never-been-offered-in-Boston-before or never-been-done-before ideas. The conservancy is not seeking submissions for existing offerings such as public art and beer gardens but activations that will complement The Greenway’s parks and events.”

The document offers as examples “a baseball batting cage, climbing wall, outdoor escape room, shared work space, mini-golf, cafe, etc.”

The parcel was originally supposed to be the home of a museum dedicated to the city of Boston. However, construction challenges – an onramp into the tunnel is part of the block – and the Great Recession appear to have scuppered the project.

“While there is a MassDOT obligation to cover the ramp on P12, the development of this unfinished area is stalled,” the RFEI states. “A joint MassDOT-BPDA community process endorsed a park for the site but has not progressed further. The conservancy has implemented light-touch improvements and temporary activations and hopes that the activation will enliven the space while this parcel remains in limbo.”