The Vanajanlinna castle was designed by architect Sigurd Frosterus. (The Stockmann department store in Helsinki is his most important architectural work.) The architecture of the castle area reflects architectural trends from around 1910 to the turn of the 1920?s, with touches of Baroque and Renaissance, as well as their more modest Nordic adaptations. The castle has also features of the English manor building.
The construction of the main building began in 1919 and was completed in 1924. The construction took place in slow tempo mostly in summertime. A narrow-gauge railway was built for the transportation of construction materials on the site of the present road from the Harviala halt.