To search the gardens in From the Darkness in the Ghost of Tsushima drop down to the gardens and follow the wall on the right. Keep going through the tall grass, wait for the guard on the left to turn around and leave and drop down.
Keep going ahead, climb up the ladder and assassinate the archers on top of the tower. Walk across the rope to the other side of the gardens and drop down.
Go up to and squeeze through the crack in the wall.