Morning
The Castle of the Counts
Start at Gravensteen, the stone castle the Counts of Flanders built in the twelfth century. It sits right in the old town, moat and all. Walk the ramparts for the best view over the rooftops, and give yourself about an hour and a half inside.
Midday
Lunch by the water
Cross over to the Graslei and Korenlei, the two quays facing each other across the Leie. Grab a seat by the water, or take fries to the canal edge like everyone else.
Afternoon
Towers and a boat
Climb the Belfry for the view, look in on Saint Bavo's Cathedral, then take a short boat tour along the canals before the train back.