Fill the trunk of your car with helium balloons. Drive to a romantic spot in the country to go for a walk. The ideal spot is somewhere up high with a clear view of the surrounding countryside. Get out of the car and act as though you are about to set off for your walk. Make sure your partner is closer to the car than you and then throw her the keys and ask if she can get your jacket from the trunk while you tie your shoelace. When she opens the boot the balloons will be released. You can also place a sign saying, "I Love You" on the inside of the trunk so that it will be revealed when the trunk opens.