Tønsberg Fortress was a medieval fortress and castle, located in Tønsberg, Norway which was defended by the fortress for over 300 years.

Tønsberg, historically Tunsberg, is a city in Tønsberg Municipality in Vestfold county, Norway. It is located about 102 kilometres south-southwest of the capital city of Oslo on the western coast of the Oslofjord near its mouth onto the Skagerrak. The city is the most populous metropolis in Vestfold county. Tønsberg also serves as the administrative centre for Vestfold county and the seat of the County Governor of Vestfold og Telemark.