Make a map that can be given to kids who are new to your area.
Go out with a trash bag and collect trash. Turn the items into a piece of art and try to get it featured in your local newspaper as a way of demonstrating any problems of consumption and waste...
Photograph places where the 'wild' is taking over from 'civilisation'.
Make it feel like you are experiencing déjà vu
Walk (or drive or cycle) between one neighborhood and the next. When do you know that you’ve definitely moved from one to the other?
Create Land Art from natural things you can find on the beach.
Go for a walk. At each junction flip a coin to decide which direction to go next.
Design a memorial to remind people of you.