Yup.
We've got intel on tunnels too, don't we?
I wonder why the walls go so deep. Would that mean that walls existed far earlier than told and with time and sedimentation, humanity continued to build them higher?
What would be the need to have walls going far under the surface? We've not yet seen a titan that is able to dig, should we anticipate that?
The other info we got from that is intel management.
For some reason, there are spies everywhere and you can't even voice once something unusual about walls or any classified topic.
But at the same time, none of those spies has been apprehended or spilled the beans for centuries.
That means everything is incredibly well structured in that world, and the truth behind Titans and all is well protected.