Bristol Doors Open Day (13/09/2008) and Heritage Open Days (11/09/2008 - 14/09/2008) across England. Buildings and sites that are normally closed to the public are flinging their doors open offering everyone a look into a normally hidden world!
Venues include tours of the Clifton Rocks Railway and a guided walk across the Clifton Suspension Bridge. Also many other sites from the Wills Memorial building to the Avonmouth Sewage Treatment Works, all free! Please note that most sites are open for only for 1 of the 4 days, mostly Saturday - check directorys for opening days and times.
Full list of sites in Bristol can be found
here.
The list of all sites across England is
here.
Note that the tours of Bristol Temple Meads are fully booked. 
TLM