Instructions
Go to Lookout Point, which is located at the crossroads just south of Bowerstone.
Examine the statue at the center of the crossroads at around 9 p.m. at night in-game time by pressing the "A" button. You can determine the time by looking at the sundial clock on the menu screen. It will be the correct time when the statue has turned to face north, toward Bowerstone.
Travel along the road north into Bowerstone South. Go to the north side of the tavern located in the middle of town to find the cellar door.
Open the cellar door with the "A" button. After examining the statue at Lookout Point the cellar door will remain unlocked until morning.