On a left hand drive car (U.S.), it's located on the right hand side of the car, just in front of the center console. It's slightly above and to the left of where your left foot sits when your sitting. You have to remove the plastic cover right next to your left foot.
You have to remove the forward most console extension cover located in the footwell. The console extension cover has 1 t20 screw. The plastic console cover has plastic tabs that snap in towards the shifter and tabs that fit into slots at the firewall. so start by removing it towards the shifter. Then pull it out and toward the back of the car to get it clear of the firewall. If you have a footwell light on that side, disconnect it.
The filter door is located just above where the top of the console plate and near where the footwell light were located before the panel was removed. It has lattice ribbing on it. The latch (actually plastic tab) is located on the middle of the left hand side of the filter door.