I am lucky enough to live in California where the weather is pretty mild. As a result, I tend to do lots of outdoor cardio. There are some crazy spots I have found to do this.
Signal Hill is near to Long Beach, California. It has a hill (see the picture for this article) that is extremely steep. Simply walking briskly up and down that hill will give you an amazing cardio workout.
Western High School
Western High School in Anaheim, California has a stadium (used for football) and climbing those stairs will give you an amazing cardio workout.
Santa Monica Cliffs
Santa Monica, California has a staircase from the beach below up to the promenade area. Yet again, this is a great outdoor cardio workout–running the stairs.