You head up to the top of this already tall tower and then you can head outside at the top.
Been twice - both times windy as hell which was scary in its own right.
We went on the X-Scream(?) which shoots you off the edge of the building with a slight drop. We sat at the front and they made me take off my specs which made it even more terrifying as I saw everything in blur. Would have like to enjoy the views and with things in focus it may have made me poo my pants!
The other was the one that shoots you up in the air and lets you free fall a little with the ride and then shoots you up again. That was fun and the views at dusk are amazing. I love that you can look out and see all the lights and then you look a bit further and there's nothing - darkness reigns.
At the time we went, it wasn't too busy at all. Quite pricey though mind you.