My son has a couple things that he especially focuses on - one is elevators (another is hotels - but I think that is because they usually contain...elevators!). Think about it - elevators are cool. I remember the first time he really noticed one. I can't remember where we were - it was a hotel in some city and we were sitting in the lobby (probably waiting for my DH to hit the men's room). And I just was looking at my son, and he watched a man get into the elevator. The doors shut for a minute or so. The doors opened. And the man was GONE. He looked at me with this wide eyed expression. It's been love ever since. Luckily he does not need to actually ride them any more. He likes the doors and number panels best. He and his sister were "playing elevator" in our room on vacation. The closet doors were huge mirrored things that slid back and forth on tracks. They loved it!
More recently, our living room looks like a scaled down version of Boston. The Prudential Center, Customs House, Marriott - all in old boxes. I have built and constructed more elevators and diaramas of elevators and buttons for closet doors to make elevators than most folks. I think, by this point, I should qualify for a pension at OTIS (and yes, we have called them and NO they don't make minitures for sale).