The event on Saturday is billed as a rare chance to discover some of the nation's hidden architectural treasures.
As part of its Heritage Open Days, the trust is offering free admission to buildings which are usually closed to the public or charge for admission.
The trust is inviting visitors to discover and share their stories, with genealogists on hand in some properties to help people trace their family tree.
A series of events at historic houses, gardens and other properties across the country will include oral history recordings, workshops and family history "taster" sessions.
To support the events, the trust is be launching a major online resource to provide a wealth of hints and advice on researching your family history and heritage.
The site will include a "surname profiler" to discover the roots of your name, a memory map on which to upload and share your memories, and top tips from family history and genealogy experts on researching your family tree.
Fiona Reynolds, director general of the National Trust said: "Everyone's lives have shaped our collective heritage and increasing numbers of people want to know more about their past and to explore their roots.
"Whether you have memories or experiences you want to record for posterity, would like to hear those of others, or are tempted to begin researching your family tree, there are lots of ways to get involved."
Last Mod: 08 Eylül 2007, 11:10