Hey, Sherlocks: A self-guided spy game you play on your smartphone starts here at Janine's.

Whistle-blowing has been a hot topic this week, thanks to NSA leaker Edward Snowden. Now theself-guided, interactive spy game-slash-art project "Invisible City" invites players to track a virtual one, taking place within a four-block radius inside the North Loop 'hood.

It starts at Janine's Coffeehouse on N. 1st St., where the whistleblower has left you a message about what to do next, and ends at Dunn Bros. The app allows wannabe Harriet the Spies and Encyclopedia Browns to scan objects on cue and get embedded info, some of it in video form.

Instructions include using later-model phones, turning off auto-lock, and bringing headphones, two quarters and something to write on. Read full instructions and tips here: http://www.startribune.com/a2303

Invisible City was created by digital artist Sean Kelley-Pegg, who recommends it for "gamers, Fringe Fest fans, adventurous people who don't mind opening strange doors to see what's behind them." It only takes about an hour to complete, as long as you play it while the co-operating businesses are open.

The project, funded mostly with a $7,000 grant from Forecast Public Art, was first launched last fall but didn't get too far due to cold weather and unfortunately timed construction. It will be playable through the end of June.