Indeed, so difficult was the nature of the site that the chapel took seven years to build, though a contributory factor in both time and budget was the "sheer opulence"[3] of its interior.

Lord Whitworth contributed the centre portion of the large stained-glass window above the altar, which he had purchased while in Paris,[4] and which reputedly had come from Russia (he had been plenipotentiary in St. Petersburg in the 1790s).

All the interior vaulting and columns are cast in timber and feature a paint wash (faux pierre) to give the effect of stone.

"[3] The exterior was clad in a thin layer of "fine limestone from Tullamore quarry",[5] and famously features over 90 carved heads, including those of Brian Boru, St. Patrick, Archbishop Ussher and Jonathan Swift, done by Edward and John Smyth.

Before the completion of the Chapel Royal, the Lords Lieutenant their entourage and hangers-on sometimes attended St. Werburgh's Church at the rear of the Castle to the west.

[7] As each Lord Lieutenant left office, their coat of arms was carved on the gallery, and then, when space ran out, placed in a window of the chapel.

It was noted by Irish nationalists that the last window available was taken up by the man who proved to be the last Lord Lieutenant, the 1st Viscount FitzAlan of Derwent (himself a Catholic).