House Rome is an annual event that in a single weekend allows the free opening of hundreds of buildings of the Capital notable for their architectural and artistic peculiarities. You may visit historic palaces, private residences not normally open to the public.
It's a chance to find detailed information on the visiting programs. Check their Facebook page that is the most up to date, and their website.
Links are below:
https://www.facebook.com/OpenHouseRM
http://www.openhouseroma.org/pagina-base/cose-openhouse-roma.html