I hate to bring Jeff Bezos into this otherwise wonderful discussion about eating trashy food from home, but:
Not a lot of great routes without traffic in the city, but there are a lot of possibilities outside the center. The following website lists possibilities and although many are for distances greater than 20 km, you could easily shorten the trip. There is an option to narrow down the choices using the included links. https://www.bikemap.net/en/l/3176959/