The period sept 6th-9th September is this year's Heritage Open Days event.
What this means is that a number of historic buildings, not normally open to the public, are accessible and that some builidings you would normally have to pay to enter are free of charge. The National Trust and English Heritage will have some of there most famous properties with free entry. Keep your eyes on the registered properties because new ones will be added.
For me the great thing about this is that 3 local churches, that are in my targetted 1000 to visit, will be open. These 3 are normally locked and getting hold of the key is difficult. So one day that weekend I'll be devoting to finally visiting these churches. There is another local church that I have yet to visit and that is only 10-12 on Saturday's in Summer Months I really must do that soon.