CITADEL

[noun] [C] - a strong castle in or near a city, where people can shelter from danger, esp. during a warThe town has a 14th century citadel overlooking the river.A citadel is also a powerful organization in which finding a job is difficult for someone who does not know people who work there.At the age of 32, she managed to enter/storm one of the citadels of high fashion.