Complex sentence: The Library and its sister institutions, the New York State Museum and New York State Archives, are housed in the Cultural Education Center, which is part of the Empire State Plaza, a large complex of State government offices in downtown Albany, New York.
Split into simpler sentences: The Library and its sister institutions, the New York State Museum and New York State Archives, are housed in the Cultural Education Center. The building is part of the Empire State Plaza, a large complex of state government offices in downtown Albany, New York.