House of Lords and the undercroft
The plan was prepared in 1794 by the famous architect Sir John Soane as part of a scheme to provide better ventilation for the House of Lords. This cross section of his proposed heating system shows the undercroft beneath the House of Lords where Fawkes had stored the gunpowder in 1605.
John Soane's Plan for Warming and Ventilating the House of Lords
30 June 1794
Parliamentary Archives, HL/PO/JO/10/7/980A