I didn't plan this route too much before I did it. I had always wanted to ride out to the Pt. Reyes Light House and I didn't think it would be that long, so I decided to go over Mt. Tam and go down the west side (which I've always been meaning to go on). It ended up a little longer than I thought. Luckily, it was a beautiful day with not much wind. It took me a little over 10 hours door-to-door do this 120 mile route.
A deer almost hit me on the backside of Mt. Tam, a lady in a station wagon almost turned into me in Inverness, and there's no water between HWY 1 and the lighthouse (well, perhaps you could turn off at one of the beaches). The last 10 miles to the lighthouse is all cows, cows, cows, which is fine, I like cows. The lighthouse and views are beautiful (although if you actually want to go in, the lighthouse is closed on Tuesdays and Wednesday).
This is the first route I made with my Garmin 205 Edge that I received as a gift for Christmas. I assume it's pretty accurate and it's a lot easier than making these things manually.