Forts for the Node War can be purchased from
Black Desert Silver in any major city. Forts function like a command center
in the Node War. It is an automatic loss if the fort is destroyed, and you will have to leave the battlefield immediately. Therefore, it is crucial to build and protect your own fort as much as possible while destroying the other guilds’.
There are two kinds of forts, and you can choose one of them. Purchase a [Node Fortress] from a guild management NPC, and install the fort at http://www.blackdesertsale.com/ .