Save your game at the glowing crystal before entering the staircase. The new patch removes auto-saves.
As Lucia's level drops into the mid-tier range, standard enemies will pose an actual threat to her. Balance is crucial here: if she dies prematurely to basic mobs, you face a Game Over. You want controlled, tactical defeats. The Subterranean Ruins (Target: Level 75 to 50)
Select "Offer the remaining royal jewels" (+5 Gideon AP, +5 Corruption).