Chateau-sur-Mer is the first of the grand Bellevue Avenue mansions of the Gilded Age mansions in Newport, Rhode Island. It is now open to the public as a museum. Chateau-sur-Mer's grand scale and lavish parties ushered in the Gilded Age of Newport, as it was the most palatial residence in Newport until the Vanderbilt houses in the 1890s.

Chateau-sur-Mer was completed in 1852 as a French villa for William Shepard Wetmore, a merchant in the China trade, who was born on January 26, 1801, in St. Albans, Vermont. The builder was Seth Bradford; the structure is a landmark of Victorian architecture, furniture, wallpapers, ceramics and stenciling. Mr. Wetmore died on June 16, 1862, at Chateau-sur-Mer, leaving the bulk of his fortune to his son, George Peabody Wetmore. George later married Edith Keteltas in 1869. During the 1870s, the Wetmores departed on an extended trip to Europe, leaving architect Richard Morris Hunt to remodel and redecorate the house in the Second Empire style. As a result, Chateau-sur-Mer displays most of the major design trends of the last half of the 19th century. The house is constructed of Fall River Granite. Unlike most of the "cottages" built in Newport during this period, Chateau-sur-Mer was one of the few built as a year round residence. This was because the Wetmores were a New England family who made Newport their home. George was very active in Rhode Island politics during the late 19th century. A life long Republican, Wetmore was a member of the Electoral College of 1880 and again in 1884. In 1885 Wetmore was elected Governor of Rhode Island, and went on the win re-election in 1886, but was defeated in an attempt for a third term in 1887. In 1894, the Rhode Island General Assembly elected Wetmore to the United States Senate, where Wetmore remained until 1913. In the Senate, Wetmore served on the Naval Affairs Committee and the Appropriations Committee. The house was added to the National Register of Historic Places in 1968 and purchased by the Preservation Society of Newport County in 1969. In March 2006, Kathleen Styger and Michelle Styger, as interns for the Preservation Society of Newport County, conducted extensive research for descriptions on the interior of the Chateau-sur-Mer estate as part of the National Historic Landmark nomination submitted to the Department of Interior resulting in recognition as a National Historic Landmark. It was declared a National Historic Landmark in 2006. The former carriage house and stables for the Chateau-Sur-Mer estate are owned by Salve Regina University and are currently being renovated as a center for visual art and cultural and historic preservation known as Wetmore Hall. Two HABS photos and one other older photo are available.