Hallwyl House at No 4 Hamngatan was built between 1893 - 98 to designs by Isak Gustaf Clason (1856-1930), Sweden´s most renowned architect at the time. Among his other works is Nordiska Museet (The Nordic Museum). Walther and Wilhelmina von Hallwyl wanted a Stockholm home built to their own specifications; Wilhelmina needed ample space for her steadily growing collections, and for Walther there was to be an office wing from which he could run the family business empire. During the years of construction, Wilhelmina kept a close watch on progress and often visited the building site.

Clason was, however, entrusted to choose a suitable style for the building, and he opted for a combination of Venetian Late Gothic and Early Spanish Renaissance, creating in effect a Mediterranean "palazzo" in the centre of Stockholm. Clason´s eclectic approach is also evident in the interior - the main rooms were decorated in a variety of styles.

Unhampered by any budget restrictions the architect was able to use only the best materials and the most skilled craftsmen. The total building cost in 1898 was more than 1.5 million Crowns, making Hallwyl House one of the most expensive private residences ever built in Sweden.

In contrast to the architecture of the house with its references to past styles, all manner of modern technology and conveniences were introduced at the outset, such as central heating (a hot air system) and electric lighting in every room. Hallwyl House was probably the first domestic building in Sweden to be thus equipped.

In 1920 Walther and Wilhelmina von Hallwyl donated their Stockholm mansion with its contents to the Swedish State. The terms of the bequest stipulate that the house must remain essentially unchanged. Behind the facade of No 4 Hamngatan the wondrously preserved series of rooms as originally furnished by Wilhelmina von Hallwyl affords a unique testimonial of the lifestyle and décor of the late Victorian period in Sweden.