Rent Bikes and just head for the mountains. Start with the Shanti Stupa as your first destination. You can rent a jeep and drive the bikes up to Khardung La, the worlds highest motorable pass at 18,380 ft and then ride (fly) the bikes back to Leh. Be sure to be at the first army checkpoint before 10:00 AM or you will not be allowed up to Khardung La.