Ends Sunday, 20 September, so not a lot of time to arrange an actual visit, but forty-eight hours in which to visit online.
https://www.heritageopendays.org.uk/

Select 'visit' in the top banner, scroll down the page a tad, and then you can select events in a town, county, and select online events only. There must be at least one place which will interest you because there's seventy-one pages of online events.

Pam