The apartment is located in Charterhouse Square in historic Clerkenwell. It is on the western edge of the City of London, just east of Smithfield Market. Close by is the oldest church in London (St Bartholomews). The neighbourhood is rich in all manner of restaurants, cafes, pubs - buzzy, but rarely too busy during the working week, and quiet at the weekends. Nearby for high class 'culture' is the Barbican Arts Centre which has cinema, theatre, music and art.
The general location of the flat is hard to better. Pretty much the whole of central London in (half hour) walking distance - Islington to the north, St Pauls and the river to the south, Covent Garden, Bloomsbury, the West End, to the west.
For transport, the Barbican Underground station is round the corner. This gives access to the whole of London underground. It is one stop from Farringdon (for trains to Gatwick and Luton airports) and two stops from Kings Cross/St Pancras (for Eurostar to Europe, underground to Heathrow, and trains to the north of England).