The map is designed to force players to make quick decisions. The idea is the survivors and the zombies all spawn outside, and the humans have to figure out if they want to run for the watermill, the hollow tree or another location quickly. Wherever they go, they likely won't be at their destination long before making another choice. If they went to the mill, they can follow the drip leaves, or make the jump for the haybales. From the tree exit, they may decide for the pond or the haybale to the right. Most likely, this second choice will eventually lead them to the cavern behind the waterfall, where they can make their final stand in either the upper or lower section.
There's also two secret hide-aways beneath the water. One, at the end of the pond that's meant as a desperate escape attempt, they must swim through. The other is beneath the lily pads and functions similarly but has a risky escape route into the main cavern.