This is a dangerous area containing the slender zombies, which are tall, teleporting, glowing eyed zombies. It is fenced in, and it contains the altar. Once the player enters the tall grasslands, creepy wind chime music will begin playing.
It is toward the end of the tall grass area, and the area around the Altar has no tall grass. On the top of the altar is the Cursed AK47. When picked up, a horde of slender zombies will spawn on the player.