Strata SE1 (known in development as Castle House and informally known as The Razor, and sometimes locally nicknamed Isengard ) is a 148-metre, 43 storey, 408 flat skyscraper at Elephant and Castle in the London Borough of Southwark in London, England. Designed by BFLS, it is one of the tallest residential buildings in London and will be home to more than 1,000 residents.