Foxes, deer, sheep, and wheelie bins can all leave trails. Find one and track down its owner.
Use some skateboards to hold a dry swimming championship.
Put on a performance for a CCTV controller. You could improvise a short play, show off a dance routine or hold a full blown talent show.
Make a giant sign.
Start at one end of your local high street and find the letter 'A' in a shop name, and then 'B', until you find 'Z'.
Travel 100 metres without being seen.
Climb to the top of the world's highest places without leaving home.
Put identical containers outside in different places when it's raining... does one fill more than the other?
Paint a stone red. Leave it somewhere and then come back at a later date to see if you can find it again.
Cut eyeholes in a newspaper and then secretly follow some friends.How long can you go without being seen?
Explore your local area looking for signs and words that command you to do things. If you find one, do what it says.
Post paper blog entries on your street.
Ask some old people you know to hang out in hoodies on a street corner.How do people react to them?
Don't turn anything on for a day (and you're not allowed to ask anyone to do it for you!)
Walk down your high street and turn to stone every time someone with a beard looks at you. Record how many times you freeze there.