Leslie promises to turn Ann's construction pit into a park.
The promise is made in the pilot episode after Ann Perkins attends a Pawnee town meeting. Ann wants the dangerous pit beside her house filled in because her boyfriend, Andy Dwyer, fell into it and broke both legs. Leslie Knope sees the complaint as an opportunity to create a public amenity rather than merely remove a hazard.
Leslie makes what is essentially a “pinky promise” to fill the pit and build a park there. The project becomes the first major civic mission of the series and introduces the show's central tension: Leslie's enthusiastic belief in government versus Ron Swanson's deep skepticism of it.
The pit is not just a one-episode plot device. It anchors early storylines involving permits, public meetings, competing proposals, and Andy's absurd attempts to remain connected to Ann. The eventual park, Pawnee Commons, also gives the series a long-running symbol of Leslie's determination to improve her community.