This tunnel entrance in Scotland must be thirty - forty yards high (Opinions welcome), and it connects to a tunnel system that criss-crosses Eurpoe and ends up in Turkey.
All I can say off the top of my head is that the entrance wasn't built for humans to walk through, not even if the humans were 12 feet tall, as Olaf describes the hollow earthers.
Maybe it was built for vehicles, big ones.
I have heard of the Scotland to Turkey tunnel complex before, but I never saw an entrance so huge associated with it.
I just don't know what to think.