I don't remember the entire course that I took for my first century... I think it was in 1996 (when I was 20). I rode the thing on my mountain bike, with knobby tires. What a great idea!
I do remember that I started from home (in north San Jose), and rode through Los Gatos and Palo Alto among other local towns. And I vividly remember how sore my butt was after the ride! And that I could barely walk the next day, so I sat on the couch watching football on TV.
From little things, big things grow... I've gone on to do quite a few rides of 100 miles or longer.