The widest house in Amsterdam can be found at Kloveniersburgwal 26 near Chinatown vicinity. Known as the Trippenhuis or Trip House, it is a dark looking building with intricate cornices measuring 22 meters wide.
It was built in 1660–1662 for the wealthy Amsterdam weapons traders Louis and Hendrick Trip. The building was designed by the architect Justus Vingboons as a double house to accommodate two brothers and their families built behind one single seven-window-wide façade. To be precise, Hendrick Trip and his wife Johanna de Geer moved into the northern house and Louis Trip and his wife Emerentia Hoefslager into the southern house.
According to Wikipedia, the famous painting called the Nightwatch, by Rembrandt was once hung here until 1885 before being moved to the new Rijksmuseum.
At present time, The Trip House is occupied by The Royal Netherlands Academy of Arts and Sciences. https://www.knaw.nl/en
Note: The Little Trippen House is across at number 29.