The quest says its unknown but its Big Ben ClockTower. I think i mist some thing in Katz's Lab after i defeted him. So i can not get in to Big Ben tower yet. Any advice on what i missed!!!!!! please help
When you finish Katz lab you will be sent to the Royal Museum to talk to the guys in the lobby. Then you go to Counterweight East and West in turn (upstairs in museum); you should be able to get in and get instructions from a helper inside. Once both of those are done you can enter Big Ben.