Right, I forget that the concept of Thule changed over time.

And yeah, they were definitely aware of the world outside of their own cartography. I believe there were definitely accounts of them attempting to journey on the Baltic Sea, but I don't recall it ending well.

Similarly they also were well aware of the Chinese. It's disputed but Roman ambassadors or merchants made it to China at one point. I believe in 166 BCE a crew went over there, but unfortunately they likely returned home at a troubling time when the Antonine Plague was spreading.

Might be wrong about some details though.