An old royal palace once stood on the site, but the 18th-century building that finally replaced it was the work of Sir William Chambers (1726-96) during the reign of George III. It was built to house government offices, principally those of the Navy; for the first time in more than 100 years these gracious rooms are on view for free, including the Seamen's Waiting Hall and the Nelson Stair. In addition, the Navy Commissioners' Barge has returned to dry dock at the Water Gate. The rooms are on the south side of the building, by the river, and the Courtauld Institute Gallery occupies most of the north building, facing the busy Strand. Between is the cobbled Italianate courtyard, where Admiral Nelson used to walk, which is the scene of an ice rink in the winter holiday season, as well as summer concerts and other cultural events. Cafés and a restored river terrace adjoin the property, and a stone-and-glass footbridge leads up to Waterloo Bridge, which you can walk across to get to the South Bank.

In the vaults of the house is The Gilbert Collection, a museum of intricate works of silver, gold snuff boxes, and Italian mosaics. The micromosaics on tables, portrait miniatures, and jewelry are made in such fine detail that you might think they're painted, so be glad if you're offered a magnifying glass -- it's the best way to fully appreciate the fine detail. The Hermitage Rooms is the showcase for a selection of rotating exhibitions from the collections of the State Museum in St. Petersburg, and other Hermitage-related activities. The opening show consisted of a selection of jewels, antiquities, portraits, and miniatures amassed by Catherine the Great, one of the greatest collectors of all time. Subsequent exhibitions have included masterpieces of the Walpole Collection: Britain's first Prime Minister amassed works by artists such as Rembrandt, Rubens, Van Dyck, and Poussin, which were then sold to Catherine the Great. Ironic that these pieces returned to the country for the first time in more than 200 years. COST: Somerset House free, Gilbert Collection £5, Courtauld Institute Gallery £5, Hermitage Rooms £6. Visit two collections, save £1; visit all three, save £2. Tube: Charing Cross.