Start/Finish is at the parking lot at the intersection of Sunset Blvd and Lake Merced Blvd (see detail maps below).  

There is no address for the parking lot.  Most navigation devices allow you to input an intersection (Sunset Blvd and Lake Merced Blvd, San Francisco)
You can also use the address of a house across the street 280 Gellert Dr, San Francisco.  That will get you close enough to see the parking lot
Or, if you prefer the actual coordinates   37.728139, -122.493525

The full marathon is 6 laps - 4 full laps, and the last 2 laps cuts across bridge near the south end of the lake.

The course is relatively flat with a few small rolling hills (nothing major). It is a paved course that is away from traffic. There is a small groomed dirt trail on the side of the paved path that many runners prefer to run on. There is a porta potty and an aid station stocked with water, Gatorade, sweet and salty snacks every 4.5 miles. There is also a water fountain and porta potty near the 2 mile marker (on this map). 

The race director, co-race director, or volunteer will be at the aid station to mark your laps and have you reverse direction each lap

Lake Merced

Start/Finish Line

Start/Finish Line