The courtyard at Southwark Cathedral, set back from the Thames, is a particularly welcoming patch of green in the built-up environs of London Bridge. There's been a church on this site since the 7th century. The current version is medieval (with a few 19th-century additions), and was the first church in London to be built in a Gothic style. It took shape slowly over a 200-year period between the early 13th and the early 14th centuries, and by the 17th century lay at the heart of the theatre district, just downriver from the Globe and Rose theatres. It wasn't redesignated as a cathedral, however, until the early 20th century.
Inside are memorials to Shakespeare (who is believed to have worshipped here) and Sam Wanamaker -- the American actor-director largely responsible for rebuilding the Globe Theatre. Organ recitals are given here on Mondays at 1pm, and classical music recitals on Tuesdays from 3:15 to 4pm. Both are free.