Super simple achievement here, you just have to unlock the forest (the pack a punch area) by round 7. To unlock the forest you need to collect the three tuning forks across the map by completing three challenges. You can begin these challenges by breaking three vases across the map and filling them with souls (killing zombies near them). One challenge requires you to survive a small wave of vampires by one of the perk statues, one requires you to slowly fill up a clock circle on the ground by standing in it, and the last one requires you to find a ghost hidden somewhere on the map and follow her to where she'll give you the tuning fork. Bring all of these tuning forks to the courtyard area and to the gate covered in prima materia (I assume thats what it is), and if you did it by round 7, the achievement will pop. Here is a very short and simple video with all locations for the vases, perks, clocks, and ghost spawns.