1. Map Room
You can drive right through the map room at a field. However, you cannot drive through the "false map room" that looks just like the real one, but serves no apparent purpose.
2. Tunnel Jumping
If you're on top of a tunnel and drive off so you fall into the ramp area, you land straight on your nose. However, no damage occurs.
This was all done with an M3. Didn't check other GVs.
