It is described by Eshonai in stages. She takes in the lower level and finds it to be marked by broad hallways and galleries, lit by carefully cut gemstones that make light sparkle. She notes that chandeliers hang above her as broken suns spraying light everywhere.
Further, she notes that the upper floors are more like tunnels. Narrow stone corridors, rooms like bunkers dug into a mountainside. In passing several rooms, she notes that there is one with paintings on all the walls, then one with a bed and furniture. Another door reveals an indoor privy with running water, which - to her - is a marvel she doesn't understand.
To Adolin, though the depths of the palace feel like caverns, the entryway is glorious. Walls of marble, polished and reflective. Grand staircases, and a bright red rug down the center. He'd burned that as a child once, playing with a candle.
To the west of the entryway is the palace garrison, a large housing for soldiers.
Gone is the ornate, but boring (according to Venli) human fortress. In its place stands a grand construction that used many of the original foundations and walls, but expanded upon them in a unique design. Instead of boxy lines, it contains grand arcs, with large ridges sweeping down from the sides like curved blades.