If you are trying to cite information from a museum website, such as a museum written description of an artwork, it is recommended to cite it as website with the museum as the author in addition to having a reference for the actual artwork.
For APA, I would use the following format:
Name of Museum. (date). Title of webpage. Retrieved from URL
Here is an example using Jackson Pollock's Number 5, 1950, which is owned by the Cleveland Museum of Art: