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One approach is negotiating with the city to sell or lease the land. Another option is to have the government hold the land in a trust, akin to the Eastern Band of Cherokee model. Finally, if the government deems the land surplus or of cultural significance, it could cede the territory to Ironland, granting full sovereignty and allowing the micronation to fully realize its identity and governance.
I am not certain what these routes would actually look like in real life, but @TheRealEstateLawyer told me she'd be willing to do a deep dive on this for us if enough people were interested.