The London Open House Annual Event is a true architectural feast. This is London's biggest architectural ‘exhibition', and it gives architecture buffs the opportunity to visit over 600 buildings new and old across the city. Many of them are normally closed to the public, and there are plenty of architectural gems to see. Admission is free for all, but it is wise to check the event website beforehand to find out which buildings are going to be open, and whether it is necessary to book in advance.

Times
Various.