For a serious cardio rush and a hiker's high, hop off the Catalina Ferry at Two Harbors and make the trek up to Ballast Point.
The steep route is a little tricky to find, so I recommend asking a local to point it out. On your way back, rather than taking the rocky trek down the same way you came, follow the road that you find at the top instead. It's a little longer but provides additional stellar views of the area.
To get here, catch the ferry toward Catalina from San Pedro, just north of Long Beach, and try to make sure you get a direct route to and from Two Harbors.