Never Stand Still
The city magically shifts at random intervals; no one really understands when or why it shifts, or where it is going to shift to. It rarely travels to the same area twice.
Shift can happen anytime from instantaneously, to a very long period.
At the Oracle of the Mind temple, there is a huge sphere suspended above the temple. When the seers detect an upcoming shift, the sphere rings is a distinct manner. A countdown to the next shift is displayed on the sphere, as well as any visions the seers have detected about where the city might be going next. The longest the seers can detect a shift is usually 1 week, but sometimes they cannot detect a shift, and many a merchant and explorer has been lost outside the city when it shifts. Occasionally, the visions are wrong and the city shifts before the timer.
Those leaving the borders of Shangri-La, usually carry a magic item attuned to the sphere. When withing 100 miles of the sphere, the item will alert of the sphere is activated, and give the countdown timer and vision information.