Which chamber was directly above the explosives guarded by Guy Fawkes?

The chamber directly above the explosives guarded by Guy Fawkes was the House of Lords.

The Gunpowder Plotters rented an undercroft beneath the first-floor House of Lords and filled it with gunpowder hidden under firewood and coal. Their plan was to detonate the powder during the State Opening of Parliament, when King James I, members of the Lords, bishops, judges, and other officials would be present.

Fawkes was discovered in the undercroft during a search on the night of 4 November 1605. He was posing as Thomas Percy’s servant and carrying slow matches, touchwood, and a lantern. The search party initially found a large quantity of firewood, but Percy’s known Catholic sympathies prompted a more thorough inspection.

The Painted Chamber and Star Chamber were other important rooms in the old Palace of Westminster, but they were not the chamber directly above the cache. The House of Commons was also part of Parliament, yet the intended target was the Lords chamber, where the king and assembled political leadership were expected.