Valuable documents

Exploration Stage: Historical Museum
From: Ursula Hartley
Description: I'm looking for something that affects the exhibits or the flow of time, but I don't know which one it is. Oh, my God, can you help me? I can't open that sturdy bag. Let's see what's inside.
Completed: You opened it! Was there nothing inside but papers? Oh, these are blueprints for an airship station drawn by a collector. Our mailman hero must have delivered them to the Upper City, which was separated by a "crack". It's a priceless find!