If you have got ranked expert (note: some people report it working on all rankings), you can go to Ford Island by going up on top of the mountainous area and finding a white "e" on top of one part.
You need to go about 30Mph into it and then you will be taken to a little island about 1,000 metres away from the big island of Oahu.
Remember it only works if you are ranked expert and it is not a racing area.