GTA IV: Under the Radar achievement
GTA IV: Under the Radar is a tricky achievement to get. It involves getting a helicopter and flying under all the bridges in the game. Start by driving to the Heli Tours and stealing a helicopter. After flying under the first bridge you'll be informed there's 12 more to do for an achievement. At this point the bridges you need to fly under are highlighted on your radar and in the in game map, but only briefly so take note quickly. Interesting enough, the radio in the helicopter comes on after flying under the 2nd bridge. Strange.
All in all it took me less than 10 minutes to do (handy for YouTube). The bridges in Aldernay attract unwanted police attention. You'll see them shooting at me towards the end of the video where I start to lose concentration and hit a few things. I saved the worst bridge for last - where the helicopter gets real close to the water.