The Causeway is a heavily-guarded causeway that connects The mainland of Great Britain to Holy Island.
The Causeway will recede every now and then when the tides comes and covers it up to keep Infected out.
At the end of left side of The Causeway leads to Holy Island, which has two, big wooden doors that are held shut by a thick wooden plank at the end of The Causeway, if any Infected were to run up to Holy Island via The Causeway, there's also a lookout beside the wooden doors that are used to shoot flaming arrows out of.
At the right side of The Causeway leads to the mainland of Great Britain. There in the mainland, it is filled with infected and crazed non-infected.