I had a bit of trouble finding the autocross event held at the Marina Airport for the BMW club (who are inclusive of other cars, which is why I went) - they didn't have signs up. Hopefully this map helps others. The entrance is right before (to the south-west) of the hangar area, to the right off Imjin Rd, just past Anzu Corp. The entrance is a bit steep; if you have a low car, go slow and at an angle.