citadel
noun [ C ] uk/ˈsɪt.ə.del/ us/ˈsɪt̬.ə.del/
(BUILDING)
城堡;堡垒，要塞
a strong castle in or near a city, where people can shelter from danger, especially during a war
The town has a 14th century citadel overlooking the river. 镇上有座14世纪的城堡俯瞰着河面。
(ORGANIZATION)
literary（难以进入的）排外组织
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 one of the citadels of high fashion. 32岁时，她成功进入了一个有着强烈排外情结的高端时装设计圈。