Guild Wars 2

The last thing I need for 100% completion of Lion’s Arch is the Vista at the top of that big green construct in the square. Can someone tell me how to get into that contraption in order to get up there ? I can’t find the entrance…

Thanks !!!

I think you mean the vista above the mystic forge (on the map very near to the waypoint at the bank).

It is also at the start of a jumping puzzle. So the first 1 minute 45 seconds of this video will show you:
https://www.youtube.com/watch?v=Rm8HGypVR_M&feature=relmfu (and if interested in the jumping puzzle, just watch the whole thing).