Host can be annoying
I occasionally watch this show, being a fan of history and tunnels and mystery. But the host (the current guy, Don) irks me the way he likes to push ahead of his guide, like when they're going through a doorway. He also likes to film himself explaining something rather than the guide. Part of it seems like he's genuinely excited about what he's doing, but it also seems like he has a bit of an ego. Other than that, I think he does a good job hosting.
For awhile, I wondered if the original host got hair plugs. Wasn't the first guy balding? They seemed so similar otherwise that it threw me. (Infrequent viewer, as I said.)