The Hall of Deliberation was not underground. It was made of glass.
A dome set into the Spire's shoulder, open to the sky on all sides, the ceiling transparent enough that the clouds were completely visible from every point of the room. Tiered galleries wrapped the interior in concentric rings - officials in the lowest, captains and visiting delegations in the second, citizens filling the upper seats in a crowd that was still rushing in from the ceremony, still carrying the noise of the bridge in their clothes and their faces.
