Picture: http://imgur.com/MHtKTv0
So, attackers a attack the park and have to capture it.
Later, they must build the northern bridge and preferably build another one if they want so they can get behind the enemy and flank them.
The last thing to do is blow up the enemy HQ. Defenders can build two force fields, which can be destroyed by conventional means (explosives and ammo) eventually. Attackers can build a bridge to HQ from the neighboring building.