Any recommendations? We will be staying perhaps 3 nights in Brugges, so can head somewhere maybe 1 day. Thank you

Certainly either Brussels or Antwerp are easy day trips by train. The jury is still out on whether or not Ghent is worth it.

But my favorite day in all of Europe (which we've now done twice) is bicycling north of Brugge along the Damme Canal to the Dutch border with a wonderful stop for lunch at Siphon.

The Siphon, a culinary institution since the 1960's... Childhood memories. If you like to cycle a bit more than 7 km one way, just continue on the left hand site of the Siphon to Sluis, where you can also find some nice fish restaurants.
Bicycling in this region is something you will not regret.

Very good idea to cycle. Ask if your hotel offers bikes. Some do. If not too late, try the Adornes hotel, they offer bikes.
Or just take the train and go to Knokke for a walk in town or alongside the beach.

The Siphon is a very well-known restaurant, and Damme is a nice place to visit. If you make it to Sluis; there's an excellent restaurant there called Oud Sluis (Michelin starred).

I love the idea of biking while in Brugge...how flat is it? I am not exactly in shape, and last time I rented a bike on vacation (in Martha's vineyard) it was so hilly I ended up having to walk my bike up the hills! Can a relatively out-of-shape person bike that area easily? (I'm a New Yorker so it's not like I get NO exercise...)

It is very very very flat! Belgium is very easy to cycle; lots of cycle paths.

Have you thought of a tour with Quasimodo of World War I battlefields?

See the question a few posts away.

You can take the train to one of the coastal towns (Oostende, Knokke-Zoute, Zeebrugge ...). Nothing better than a walk on the beach to get a fresh head.