[Sherlock had tried something similar at City Hall already. He was glad he wasn't the only one to think to try the places that seem to be the root of all their troubles. It was solid as a rock. And now he sees this place is as well. He files it away for later information.]

Don't hurt yourself. I don't think it's going to let you in.

[But this is very interesting indeed. Everything else is - phasing in and out of existence, but not these two buildings. That has to mean something, right? He can only assume the same is true for the Post Office.]