There are many quirky book stores in London, but I really love the selection that Daunt Books have, they often have bespoke editions which you won't find in other book stores. Also, the people that work there are so helpful and knowledgable. I can never stop myself from walking in!
I spend many hours in the bookshops along this stretch, namely Henry Pordes for second hand books and new discounted titles (pile on left of photo), as well as Koenig Books for new art books with lots of great discounts in the basement. (photo right). In 2001 the rents for much of this strip were increased to align them closer to market value but thanks to public support they were reduced again. Unfortunately some bookshops still closed down; Koenig replaced the beloved Zwemmers - a real institution - but thankfully still provide great books, although others are no longer bookshops at all.
I love the architecture of the Barbican - it is so important to its historical context, at a time when London was being shaped for modernity after the war - they also aspired to make it a bold art centre. We need bold, always.