The Waterfront Lighthouse is the Imperial Legion-controlled lighthouse in the Waterfront District.
The main entrance leads into the Waterfront Lighthouse, below is the Imperial Watch Barracks, and below that is the private quarters of Velan Andus.
The top floor of the lighthouse
The entrance to the lighthouse holds a clutter barrel and chest against the East wall and four crates with the same contents against the southeast wall. A fifth crate with the same contents sits in the northwest, between the trapdoor to the barracks and the ladder to the upper area.
The upper area holds six barrels, three crates, and two non-respawning sacks, and they all hold clutter. The table on the west wall is set with two apples, two cheese wedges and a loaf of bread.
Imperial Watch Barracks
Moving clockwise around the room from the entrance from above, lying against the walls are a chest of drawers that holds clutter, two single beds, a food cupboard, and a table set with three apples, two cheese wedges, a loaf of bread, and two bottles of Surilie Brothers Wine. Another food cupboard sits between the ladder back up and the trapdoor to Velan Andus' private quarters.
Between the ladder from above and the double bed lies a chest of drawers that contains clutter with a dish that holds two apples on top and two non-respawning clutter sacks next to it. The table on the southeast wall is set with three apples, two cheese wedges, and two loaves of bread.
Elder Scrolls Wikia entry on this location can be found here.