just to be sure: "there are two ways to enter a regio voluntarily, and either or both may apply to a particular regio." (RAW, p. 189).
This means, that here are regios you can enter after seeing into OR after follow a particular path (both is possible)
And there are regios you can only enter after seeing into it (no path existing)
And there are regios you can only enter by following a path! Is it true? Can you see into a regio (with second sight, for example), that you can only enter by following a path? I don´t think so. What happens, if you use second sight at a regio-boundary you can only cross by following a path?
I think there are - and should be - regiones where you can only enter if you follow a particular path, perform some ritual or be let inside by a resident.
I don't like it if any region can be forced entry to (or exit from) that's not good story wise.
The Transylvanian Tribunal book has a covenant with regiones that can only be entered via teleportation with an arcane connection. IIRC these were deliberately sealed - presumably via secret method, though coming up with a PeVi magic to suppress Second Sight to prevent viewing a regio boundary is well within hermetic magic's capacity. There is also mention of various covenants with sealed regiones, though these are seldom described adequately to determine how they were sealed.
This could be a case of simply not having found the correct path to pass between layers (in all of the above cases). The path need not be obvious nor simple, after all.
sealing a boundary may be regio dependent as well. For example, if you have to walk down a garden path, turn to pass under the arch then walk up the steps and through the front door to enter the regio, then tearing down the arch should suffice...