How to attack "The Neck" Game of Thrones map?

Hi there, how do I access this area of the map called "The Neck" ? and attack the capital?

Here is a link to the game: http://atwar-game.com/games/?link=2384027667

Thank you

Hi, just tested the map.
The blue lines are rivers. You should be able to build a raft and slowly move up to the Neck. Here is a screenshot of two routes
https://gyazo.com/77cf9224e34f82ca409908fc6a510669