Gardermoen is a town in Norway, housing Oslo's main airport. Your only reason to stay here would be some time between flights.
Train is fast and convenient, buses may work out cheaper and have more destinations. Taxis are sometimes terribly expensive.
Save your money: Don't take a cab. Virtually all hotels here have pick up services, sometimes at a small fee. Just give them a call upon arrival.
- Kon-Tiki Kitchen, ☎ +47 64811616. Restaurant in the international terminal. Serves some pre-made hot meals for 119 (small portion) /159 (huge portion) NOK. Not too tasty, but works. On the second floor there's both power and free internet (Ask the cashier for username/password) edit
- Gardermoen Hotel B&B  is an airport hotel, 10 min drive from the airport. In June 2008 the price was 1800 NOK for two double rooms with a pick-up and drop-off service to the airport of 4 persons, breakfast included. You can book a pick-up and drop-off service separately for 45 NOK/person.
- Gardermoen Airport Hotel, (3,5 km from the terminal), ☎ +47 6394 0800 (email@example.com), . Free wi-fi and airport shuttle bus at least once an hour. Single from NOK 700. edit
If you have more than a couple of hours between flights, Oslo is within reach by the Airport Express Train. A somewhat closer, and cheaper, option is Eidsvoll, a lakeside town where the Norwegian constitution came to light.