Willis (Sears) Tower Skydeck
Made a visit here on a whim... I haven't been up here in probably 25 years or more. It doesn't matter how old you are though— it's still amazing. If you don't mind spending $19 for an elevator ride, I'd definitely recommend it as there are only a few places in the world to get this kind of vantage point.
FYI I didn't, and will never, ever, step out on the transparent death ledge.