FFXII - Walkthrough - Nalbina Dungeons
First order of business, as always - save your game. Nothing worthwhile in this area other than "Knots of Rust" (FFXII's joke item), so head to the next area.
Cutscenes, and then Balthier and Vaan vs. 3 Seeqs. Oh, you have no weapons and no inventory, either, but it shouldn't be a problem. If you got magic you can still use that, at least.
Cutscenes; next area, move toward the save point and you'll not only receive all your lost items/equipment, but a map of the Nalbina Dungeons too. Now you can save your game, and with the map you know where to go.
Next area is littered with soldiers, but don't worry about being spotted - you can defeat them easily enough. Though I should note that attacking a soldier may draw other nearby soldiers to the battle, so be careful.
More cutscenes - eventually you land in Barheim Passage, and Basch is your guest!