Here's the thing: Mountains make great walls to hide from prying eyes. Hence comes this plan:
1. Timelapse views from outside.
2. Some people are tasked with building massive towers and carving external features and whatnot. Perhaps a causeway to the gate? The sky is literally the limit.
3. A different group hollows out a mountain and creates a huge underground city. Another camera could be in here, but nothing is shown until completion.
"Huh, a mountain fortress. That's cool."
"Wow, that looks great!"
-cuts to inside-