Open House London is a rare opportunity to see inside some of London’s most interesting buildings. It’s on this weekend. Some buildings require tickets or email requests to enter, but many are first-come-first-served. Such as the amazing looking Boone’s Chapel built in 1682 on Lee High Road, which I hope to check out this weekend! Great photo set here by @darryl1974 showing the interior.
Greenwich Open Houses (Severndroog Castle is a great option). My sightseeing trip from 2008 is now out of date since the renovations. The Quaker Meeting House in Blackheath, or Old Royal Naval College in Greenwich are also good options.
Photo credit: Alex Mitchell on Flickr