Shoal Cave is unique in the way that  it changes with the tides. These inaccessible caves can only be entered during a low tide. Inversely, some parts can only be accessed during a high tide. The tides change during certain times of day. 
High Tide: 9:00 pm - 2:00 am & 9:00 am - 2:00 pm
Low Tide: 3:00 am - 8:00 am & 3:00 pm - 8:00 pm