Treacherous Jack is a lighthouse, located at the northern end of the treacherous coastline between the mouth of Sellen River and the mouth of the Porthmos River, known as the Jagged Saw. It is one of the series of magical lighthouses constructed by Taldans thousands of years ago, in order to protect the dense traffic along the coastline. Only a few of those lighthouses remain. Most of them are now ruins or broken relics of Taldor's glorious past. Treacherous Jack is located just west of the Harbor Watch and presiding over the entrance to Cassomir's harbor. A submerged causeway connects the magical lighthouse to the shore, making it accessible by foot at low tide. It is a stout, solid stone structure topped by an enormous flame-shaped object that glows brilliantly day and night. Treacherous Jack got its name from the fact that it randomly turns off its light and usually at the worst times. Hundreds of ships have been sunk because of its erratic function, but Treacherous Jack is a familiar and welcome sight to all sailors approaching Cassomir.