Ornamentation, generally sparse and Scottish throughout the House, is at its most extravagant in the Great Hall: yet even here it is simple and restrained, The deep coffering of the ceiling, 22 feet (6.7m) above the observer, is echoed more simply in the shallow coffering under the arcades to east and west. The palmette-andanthem ion bas-relief frieze on the entablature is repeated, again in a simpler form, on the higher frieze immediately below the cupola. The composite-order pilastercapitals with their attenuated volutes, like many features of this and other Simpson buildings, are a detail taken from the 6"'century BC Temple of Apollo at Didyma. 

The floor of the Great Hall is of diagonally-set flagstones painted in the original chequered black and white pattern - in keeping with the overall originality, providing a pleasing contrast with the beauty of the walls, arcades and ceiling. The acoustics in the Great Hall are outstanding, making it an ideal location for broadcasts, concerts, plays or other performances.

The Great Hall, like the House as a whole, is symmetrical in plan. The double doors from the Vestibule to the south, surmounted by a meander frieze under a lunette, are echoed by an outline of a doorway in the centre of the north wall, though there was never in fact a doorway here. The present appearance of the outline is as it was shown in the 1873 photograph. Several pairs of double doors are in fact false and were positioned by the architect purely to preserve the symmetry of the Great Hall. The southernmost of these doors had been removed and plastered over to allow pictures to be hung, but the doors have been restored because the Great Hall was designed to have no pictures hung in it, Under the cast and west arcades, pairs of double doors to Simpson's design, of painted yellow pine, lead to the octagonal Smoking Room, to the Private Apartments, to the Great Stair, to the Billiard Room, to the Music Room and to the State Drawing-Room.