The Kings Cross Lighthouse is at the apex of a wedge-shaped block where Pentonville Road and Gray’s Inn Road meet outside King's Cross station. The Lighthouse building is fairly ordinary, except that it narrows to only a single room wide at the rounded-off end, and of course it has that tower on top. It is not unusual to see Victorian corner buildings with a decorative feature like this, but the location and the maritime associations make this one special. The lighthouse may or may not have advertised an oyster bar in Victorian times, when oysters were cheap fast food. Although the shape is right for a lighthouse, there are only tiny porthole windows, a lost oppurtunity perhaps. There is one other lighthouse in London, on top of a Methodist church in Walthamstow, very similar in shape but with a proper glazed lantern - still lit up as a beacon for lost souls.
Almost the whole of the block is now empty, and rotting away while the site awaits development. The building is Grade 2 listed, though, so it is likely to be restored eventually. The question is how long before that gets under way, and how far will dereliction progress unchecked. The whole building is decaying: one report says there are rotten floors, dangerous stairs, leaking roofs and sagging walls. The tower is made of timber, with a zinc covering and decorative cast-iron railings around the balcony. Parts of the balcony railings have fallen off and a lot of the cornice around the top is missing. The timber structure inside must be thoroughly rotten by now.
There have been plans to redevelop the site for many years. A scheme by Richard Griffiths Architects proposed a 'Miesian' (steel and glass) replacement building behind a partly-retained facade. That is superseded by a design by Latitude Architects. Their scheme proposes a restored building with an extra floor added, and was granted planning permission in 2009 despite comments that it looked like a "hunchbacked armadillo". It does indeed have armadillo-like qualities, with a curved and stepped roof clad in zinc, and the zinc tower more or less the right shape. It actually looks quite good. You can see it here, but don't hold your breath waiting for it to be built.