The Workshop is a place to create items and Masks, specifically the cheese mask and onion mask. You must gather 2 other players to follow and repair the Breakwater on the opposite side of the map from the Gift Shop. Once you get to The Underground Pool you can follow the tunnel on the right from the entrance leading to the Cistern. There is a stairway you have to go up. Upon exiting the stairway you should see The Walled Garden
Workshop
To open the door, you must restore all the trees using the sticks scattered around. After restoring all the trees in an area, a statue piece will appear near the statue. Next, restore all the statues. This should open the gates blocking off the Workshop. To open the door you must place a Crob (You Can get one from the Cistern) onto the Crob picture on the door. You may also use the Crob Mask or Full Mask to open the door, since the Full Mask can open any door. The door will glow and then open.