Walk up to the “Do Not Open” wall in the exhibition.
Close your eyes: Imagine your city in the future. Imagine how rising seas will impact it and those who will live here then. Think about what you would like them to know. Think about what you believe someone living a century from now will need to hear from someone living here today.
Unclip a blank piece of paper and envelope from the wall and use a pencil to write it all down:  Tell them who you are. Tell them why you are writing to them. Sign it. Date it.
Fold the letter in two, kiss it, place it in the envelope and seal it.
On the outside of the envelope write: “DO NOT OPEN: 100 years”
Clip the sealed envelope to the “DO NOT OPEN” wall with the words facing out.  Stare at your envelope: Think of how your words will be received in the future.
Walk away.