224,000 square feet of space. The museum remained open throughout construction, which began in 2009. Within the property's lease lines, the extension added more than 224,000 square feet (20,800 m2) of gallery space, including an underground garage. The new wing is connected to the original building by a glass-enclosed atrium. The new wing is designed to be a sustainable structure with energy-efficient lighting, appliances, and heating/cooling. It uses 75 percent less water than a conventional building of its size, and it produces no carbon dioxide emissions during construction or operation. The St. Louis Art Museum is one of the largest art museums in the Midwest. It features a collection of more than 2 million objects, including works by Leonardo da Vinci, Michelangelo, and Rembrandt. The museum is best known for its fine arts collection but also has significant holdings of decorative arts, photography, African art, and Oceania artifacts. The museum opened its doors to the public in October 2009. It was created through a merger of the city's former art institutions: the Missouri Botanical Garden's high-profile collection along with the work of local artists donated to the Garden over time. The merged organization was named the St. Louis Art Museum to reflect its ownership of both collections.