Scandinavias largest ruin park 63 metres above sea-level. Ruins from Castrum Tunsbergis, Tunsberghus, which was Norway´s largest castle in the 13th century. The castle was destroyed in 1503. The ruin consists of a 700 metres long outher-wall with watch towers and castles, the King´s hall, built by Håkon Håkonsen, the Keep built by King Magnus Lagabøte, and St. Michael´s Church, dated 1191. The rock itself consists of rombeporfyr on limestone and also of some local stone, Tønsbergitt.
The present tower on Castle Rock was built in 1888. The first tower, built by the Tønsberg Maritime Club in 1856, burned to the ground. The original cross from the Church of Our Lady, can be seen in the tower. Mail dispatched from Castle Rock Tower has its own postmark with a special motif. The tower is 17 metres high and has the engraved signatures of three Norwegian kings.