People are being encouraged to bare their souls anonymously in north London - by writing their thoughts on a table tennis ball.
The balls will be displayed at a festival
Over the past five days, messages or poems have been written on balls and sent spiralling through a vacuumed tube network spanning one square mile.
The narrow tubes run from post offices, schools and pubs across North Wembley, converging at one collection point.
The project culminates in a festival on Saturday at Pellatt Road sports ground.
A spokeswoman for City Mined, which is behind the project, said it is about connecting different public spaces and getting people to communicate in this "slightly bizarre" method.
Some of the balls will go on display at the festival, and others will be presented to the Mayor of Brent or sent to Brussels for a similar project planned for later in the year.
Festival organisers promise live performances, local art and activities for all the family.