This guide shows how to complete the Giants Mountaintop Catacombs maze to reach the boss. I will show only the critical path through the maze to keep the guide simple. This maze might get tricky and you may feel you are running through the same place again and again. So, follow the guide properly to reach the boss.
From the Site of Grace, go down the stairs and take the first right near the summon pool as shown in the picture below.
Now go straight ahead till the end of the path and then turn left as shown below. Here you will find an elevator. Take the elevator to the lower level.
After the elevator stops, you will see the Boos Lair door, which will be closed. From there, turn left and go down the stairs. Go straight ahead to reach another elevator. Take this elevator to the lower level.
When the elevator stops, go straight ahead until you reach the room with a statue as shown below. Then turn right and climb up the stairs on the west side.
Proceed in this hallway as there is a trap here. Turn left at the end of the hallway and go up the stairs. In the next room, you will see blades coming out from the ground. Carefully cross the room and go out from the door on the opposite side. Then immediately turn left as shown below and climb up the stairs.
The stairs will lead you to an L-shaped room with creatures discharging poisonous gases from them. Cross this room and climb up the stairs. In the next room, you will see a hole on the left side as shown below. Jump down from this hole.
You will drop down to a level with a statue as shown below. Climb up the stairs opposite the statue on the north side as shown below.
Go straight ahead and you will reach a room with a hole on the floor as shown below. Drop down the hole and then turn around and go south.
This path will take you to a room with the lever near a statue as shown below. Pull the lever to open the boss door. Then jump down and go through the door as straight ahead in the north direction.
Go straight ahead and you will reach an elevator. Take the elevator to the top. After the elevator stops, go straight ahead and climb up the stairs. Then turn left and you will find the boss door open. Go through the door to reach the boss’s lair. Defeat the Ulcerated Tree Spirit boss and it will drop a Golden Seed and a Glovewort Picker’s Bell Bearing .