There are two main airports serving eastern Norway, the larger one is Oslo Gardermoen (OSL), which unfortunately is far north of Oslo while Fredrikstad is far south of Oslo. Nevertheless, there is a bus service (line F11) between Fredrikstad and the airport taking slightly over two hours. Ryanair flies to Rygge near Moss (30 minutes from Fredrikstad). Also Norwegian and a selection of charter companies service this airport. Some people find a good deal if they fly to Gothenburg instead, and take the train or drive from there. Gothenburg is even further from Fredrikstad than OSL is (though the difference in time is less than an hour), but sometimes the tickets might be better there.
It is fairly easy to get around the city as public transportation in form of bus is frequent and goes around town as well as to the suburbs in all directions from the center of downtown.
Taxi is available from the main taxi central in downtown, just opposite of the main walking street.
There is a ferry from downtown to the old town which is quite frequent. It is an enjoyable and scenic means of transportation, and you get to see the city from a different view as well, as the river offers a unique view of town. There is also an additional service to the neighboring suburb Gressvik, and a third service between Lisleby and Selbak is planned to open in June 2013. All ferries in Fredrikstad are free.
If you have a rental car, traffic is usually unproblematic, but there may be some traffic jams in the main entry roads to town around 4 - 5pm (rush hour). Be aware of parking restrictions both in the old town and the city centre.
The old fortified city, founded in 1567, and Kongsten fortress.
Go see Fredrikstad Fotballklubb (FFK) play a game of soccer at their stadium across the river from the riverwalk. Fredrikstad is beyond a doubt one of the most devoted cities in Norway when it comes to supporting their local team and the strong history of the sport in the city is well felt.
Take a walk around the Old Town, on a sunny day it is beautiful. Especially great for kids as there are grass to run on, old cannons to climb, a playground and lots of ducks to feed. Go for a cup of hot cocoa and a cinnamon"snail" at Mormors Café afterwards.
There are three coffeeshops in the city centre that make very good coffees, milkshakes, smooties etc. One is Verdensspeilet (World Mirror) right opposite the cinema. The second is Syversen Tea And Coffee and the third is Malenki, next to the cinema. All three have friendly staff and great coffee, and are great for a quick bite. If you want to stay a little longer, maybe have a beer and play a boardgame then Verdenspeilet is the best choice.
The riverwalk has a lot of restaurants and bars, and in the summertime, especially, it is a very busy area where people go to eat, drink a beer in the sunshine by the water and in general have a good time. People also come by boat, staying directly at the guest pier.