One of the landmarks of England would be the Buckingham Palace. It is the London home for the British Royal Family. Other landmarks would be the Windsor Castle, the Houses of Parliament (or the Palace of Westminster), St. Pauls Cathedral, Tower Bridge, the London Eye, Globe Theatre, Alexandra Palace and of course the ever famous Big Ben, the Royal Observatory at Greenwich., the Concrete Cows of Milton Keynes.
Not to be missed is, of course, England's most famous and ancient landmark, that, of course, being Stonehenge which stands on Salisbury Plain in Wiltshire. Some speculate that it's construction was begun as far back as 2800 BC and that it was used in order to make astrological observances. Winchester Cathedral, Portland Bill, Cerne Abbass Giant, the Westbury White Horse, Glastonbury Tor (Avalon: the burial place of King Arthur and Guenivere) Tintagel (home of Arthur). Gwennap Pit (John Wesley), St Michaels Mount, Lands End, Goonhilly Earth Station, The Minnack Theatre, The Eden Project, Jamaica Inn, Dartmoor Prison and National Park. Cheddar Gorge, Anne Hathaways's Cottage at Stratford. Sherwood Forest, Chesterfield Crooked Spire, Gloucester Cathedral (Hogwarts), Coventry (Lady Godiva) the Cathedral and the roof nail cross, Birmingham Bull Ring, York Minster, Durham Cathedral, Blackpool Tower, Liverpool, Crosby Beach, Angel of the North, Lake District, Peak District, Hadrians Wall etc, etc.