Citadel

The Citadel is a Tower controlled by the Combine it was built so that the Combine would have a Headquarters place type of
==Background==
The Citadel was the headquarters from which the Combine govern the Earth. 
==Trivia==
*It has its own Private Quarters For Dr. Breen.
*It's exactly 1,000,000,000 Meters tall
*It's the Combine's headquarters
*It's not for Citizens
*It's not really Small
*And also, its not Safe for Citizens
*It can also create a portal to your mom. "don't be mad bro, i didn't even mean it, seriously."
*Those birds are in fact robots.......
*You can actually see the whole city when you're on top of the Citadel.....too bad Gordon Freeman already destroy it along with City 17.