This achievement is easier to show than explain, so I highly recommend you use the video guide below.
From the main menu, go to Campaign > Halo 3 > Halo 3: ODST. Choose the mission Kikowani Station and start at Rally Point Charlie. Difficulty doesn't matter.
As soon as the mission starts, run to the Banshee straight ahead of you and get in. Fly forward, and as you exit the tunnel, turn right. Continue flying that direction until you pass the tower, then turn left.
A little way past the tower, there will be an opening to a dead end on your right side that has a lit up sign that reads "Connection Lost" or "Access Denied." Fly into this dead end and hug the right wall. On the right side of the small bridge, there is an outcropping over a door. Hover over the outcropping and jump out of the Banshee such that you land on top of the outcropping. Stand exactly in the middle of the outcropping and touch the wall. The "Siege of the Madrigal" track should cue, and you'll earn your achievement!
If you used the video guide, I'd really appreciate it if you could like the video. Thanks!