The Kurpark (spa park) of one of the most fashionable spa towns in Westphalia in the 19th century is sometimes referred to as a "museum of historicist architecture". From the first, Neo-Renaissance spa house from 1857 to the last, Wilhelminian house with Art Nouveau elements, completed just before the First World War, this grand park setting indeed reveals the main tendencies of the taste for late Historicism in Germany. The large Neo-Renaissance building of Bath II (also periodically referred to as Badehaus IV or Neues Soolbadehaus) was built on an H-plan, in reference to the earliest Badehaus I located nearby in the spa park. The Polish designer of the building, Zygmunt Gorgolewski, was at the height of his career in German countries at the time. He became architect of the royal palaces in Berlin in 1880, and already had major projects in Halle and Leipzig to his credit, as well as numerous building supervisions. His competition design for the Reichstag was awarded. In it, as in most of his large works (such as the much later opera house in Lemberg), he referred to Renaissance forms, but achieving an eclectic redesign close to the Baroque in the spirit of Second Empire France. He had already worked on various applications of Renaissance inspiration when rebuilding the castle in Gołuchów, also designing several residences in Greater Poland.

In Bad Oeynhausen, however, the influences of 17th-century French architecture are particularly evident: the contrast of red brick and stone detail in the facades, the high roofs of the alcove annexes next to the wings, enriched with dormer windows, are features of the so-called French costume, also popular in the architecture of Wielkopolska at the time.

In the centre of the building rises an impressive dome on an octagonal tambour, with rich internal decoration.

Gorgolewski was also interested in engineering architecture; the use of certain structural elements in the design of the Baths was an expression of his good knowledge of it. Unfortunately, the interiors of the building were significantly altered in the course of transformations in the 20th century.