Once they left the restaurant, Dana nudged Karl and gave a deliberate look at the crowd near the outer ledges. They couldn't open the Tiny World there and risk someone thinking it was a portal.
Common courtesy was to allow people travelling to the same area when you happened to open a portal to pass through, and it would be awkward to explain that it was actually a separate space, capable of supporting life.
That was not a common sort of skill, and there were still enough powerful people around that Karl couldn't rule out one of them trying to kidnap him to force him to teach them the way of making the [Tiny World].
He hadn't been too concerned about it with the Dragons, as they only had to ask the Blue Dragons at the Libraries if they wanted to know the answer. But others would not have that same level of access to information that an Ancient Dragon of the Dragon Church had.
