Accessing Castle Dungeon Requirements?

Hi all,

Just wanted to know what is the requirement for a clan owning castle to access its castle dungeon?

a) Castle needs a regional fortress contracted to it?
b) Castle needs a borderland fortress contracted to it?
c) A or B
c) Both


Thanks

a)

a.
and btw, borderland fort can't make a contract
when a fortress make a contract with a castle, the fortress have to pay a fee but have more items in the chest they can take every 4hours.
mostly KE but sometimes shirt/bracelet.

a.
and btw, borderland fort can't make a contract
when a fortress make a contract with a castle, the fortress have to pay a fee but have more items in the chest they can take every 4hours.
mostly KE but sometimes shirt/bracelet.

what chest is that?

its the same npc who gives u KE (when signed contract with castle)