The shadowy vaulted Undercroft of the Banqueting House was created as a drinking den for James I and his friends. At one end there was originally a 'grotto' decorated with shells, designed by Isaac de Caus.

The Undercroft would have given the King and his royal favourites a degree of privacy which was in complete contrast with the magnificent display of the Banqueting Hall upstairs. 

The shell grotto and hidden, dark spaces beneath the vaults no doubt lent the King's revels in the Undercroft an air of mystery and decadence.

Ben Jonson's ode to the Undercroft cellar

Poet Ben Jonson wrote this dedication for the Banqueting House's Undercroft as a drinking den in 1623:

Since Bacchus, thou art father
Of wines, to thee the rather
We dedicate this Cellar
Where now, thou art made Dweller

Following James I's death, the decadence continued, when the Undercroft began hosting lotteries. John Evelyn describes one gambling session in 1664, at which 'the King, Queen-Consort and Queen Mother' won only 'a trifle' – as he did himself.

On view in the Undercroft is a short introductory film about the history of the Banqueting House. At the rear of the Undercroft are some engravings of the Banqueting Hall as it was in earlier centuries, and some depicting the infamous execution of Charles I, which took place just outside.

There is also a display on Masques, which includes models of Inigo Jones's set designs, showing how the elaborate theatrical scenery worked in the Banqueting Hall.