Sky was basically a duplicate layer selected for the sky and blend mode multiply before the bw conversion, plus some fussing around for a couple of spots that got blown out in the process. My normal workflow left the sky a bit weak, and I liked the intense treatment in your original post so "kicked it up a notch".
The original RAW was well exposed so there was lots of latitude to work. At the end, for some reason it had an oversharpened feel so I added a selection mask and blurred the foreground about .3 px and burned it a bit.
BW conversion is also simple, a solid gray layer, blend mode color then a sat adj layer to darken/lighten and change the saturatioin of selected colors.
..forgot to clone out the people on the observation deck.
Andres - where was this taken?