I'm fascinated by buildings in general. I've gotten to see some interesting old building techniques in my job, but mostly I find the big projects the most interesting. Empire State Building is a given. I guess I'm facnitaed both by the thought it goes into making both the structure and the technology to make it possible to build it.
Like for example, I saw a documentary the other year about the World Trade Center, and a big part of that was what made that structure unique. That the characteristic outer beams is what held it up. Something that led to it's ultimate downfall unfortunately.
Also an extention is this are cathedrals. I don't admire what they stand for in their connection to religion, but as works of engineering they are fascinating. My favorite in Sweden is Uppsala New Judge-Church, built originally in the 1500s, but restored in the 1800s. It is exactly 118m meters tall and long. And a fantastic building. Just awe inspiring.