Complex sentence: In 1891 the building became known as Hotel Polen when the adjacent building on the Rokin was bought, which was designed by the architect Pierre Cuypers, who also designed the Amsterdam Central Station and the Rijksmuseum.
Split into simpler sentences: In 1891 the building became known as Hotel Polen when the adjacent building on the Rokin was bought. The building on the Rokin was designed by the architect Pierre Cuypers, who also designed the Amsterdam Central Station and the Rijksmuseum.