I've done it 3 times.
There is a ride profile on the main site, rosaritoensenada.com. 25 miles of near flat, then a 900 foot climb, 10 miles of rolling hills, 400 foot climb, 800 foot rather steep drop, 10 miles of flat road into Ensenada. It is always the same route -- it's the 'free' road on the map.
I wouldn't do it with a singlespeed, but there were some along every other type of bike and even rollerblades.