Hi Ellen - well I usually start in Emeryville and ride up to Richmond Marina and back - it is only 21 miles. Adding in a loop out and back both ways around the Berkeley Marina adds another 5 miles. And it is flat flat flat (except for one very small hill). It's a beautiful route - it's a multi-use path, and there are hardly any stops required so you can really keep a steady pace (or at least that is always my goal!)