The Mausoleum is an optional area East of The Dusky Woods and is part of Nate's Adventures Quest line. Initially, The Mausoleum is located inside The
Dusky Woods, but after unlocking this area, it will be come visible on the world map.
The Twenty-Fifth Secret Bonus Area can be accessed by finding the secret entrance in The Mausoleum (Nate's Seventh Adventure.)
The entrance is north of the searchable field through the door on the right. The path to the Secret Bonus Area can only be accessed after completing Nate's Mausoleum Adventure and getting the Ghostly Amulet trinket. To access the Secret Bonus Area, you must equip the Ghostly Amulet. When you do so, the gate will turn the same translucent blue as your character and you can then simply pass through it like the ghost you are.
The puzzle has 64 puzzle pieces and the bushes are level 13.
After completing the puzzle, you will be rewarded with 250 Gold and the Holy Grail.