The Great Hakurei Barrier is described as quite a logical barrier.

Gensokyo

Somehow..!!

Right..

Considering the fact that rarely, things from the Outside World get lost into Gensokyo,

I don't know what it is exactly, but...

the barrier seems like it is less like a physical wall, and more like a barrier that prevents unconscious migration.

And so, in order to go out we need to somehow not do that.