The Shard is the glass skyscraper above London Bridge, and its viewing galleries sell one of the highest public panoramas in the city. The view is the point: the Thames bends below, the City rises to the north, and on a clear day London stretches far beyond the obvious landmarks.
It is expensive for what is essentially a viewpoint, so it makes most sense on a clear day or for travellers who specifically want the high-altitude version of London. Borough Market and the riverside walk through Bankside are close by.