Travel Health and Fitness - long run suggestions in Amsterdam?

Going to try to get a long run in (15-20 miles) during an upcoming trip to Amsterdam but my sense of the city, from previous trips, is that it's not particularly well-suited for running given all the canals and whatnot. I'd probably have better luck going outside of town. Any suggestions for a pleasant route? I was thinking of hopping on a train, going out a ways, and then running back into the city.

Running I've done in AMS has been in the city & city parks and most I ran was an hour, so can't really help you too much. Have you googled or checked Runner's World for perhaps one of their marathon routes?

Cheers.