Ive had this idea of embedding signers into statues and other landmarks such that if you are in range (be that nfc, or bluetooth), the landmark would musig2 cooperatively sign events with you, so those events are dedicated to that location (the resulting npub would be 'you at that location').

You could do something similar with a radio-system with longer range (lora's bandwidth is really fucking limited, but perhaps for chat it works).

Now the point of my innitial idea was that the landmark-embedded signer only needed power and no internet connection, so i guess assuming the location-based thing has internet,there are indeed other ways of doing it, like sharing a list or whatever.