need help from ladies

I am 40+ something man- I am very interested in a single woman at work. I rarely see her as she works in another building. I have a sense she knows I am interested but hard to strike a conversation with someone you hardly see. She has no online profile. I became aware thru a friend she teaches an exercise class in my town 1 night a week. I would think it would be weird to show up but am wondering what advice you would give to try to get more interaction? (just as a friend at first)