One of the odder sights visible from the BT Tower is the former Middlesex Hospital. Most of the buildings have disappeared, leaving an expanse of bare ground; in the centre, the chapel remains.
Although it had been on the same site since the mid-eighteenth century, Middlesex Hospital was rebuilt between 1928 and 1935. However, it closed in 2005 and was demolished in 2008. Several redevelopment plans have fallen through, so the site remains almost empty.
Thanks to being listed, the Italian Gothic chapel has survived. Work began on it in 1891 under architect John Loughborough Pearson; he died before it was completed, so his son Frank took over until completion in 1929. It formed the heart of the complex, with the later buildings constructed around it. Today, it looks bereft without that context.
There are images of the interior here.