There's something particularly appealing about a place that's normally private becoming public, an exciting sense of legitimised trespass fuelled by a burning curiosity. This weekend's Heritage Open Days around the country (and next weekend's in London) provide an opportunity to look behind approximately 2,000 doors which are normally closed and, what's more, entry is free.

Lincolnshire seems as good a place to start as any, the seat of Alford's beautiful 160-year-old working windmill which stone-grinds organic flour. After a cream-tea in the hopefully sunny garden, head for St Botolph's Church in Boston, described by architectural historian Nicholas Pevsner as "a giant among English parish churches". The county's Market Rasen racecourse is offering behind-the-scenes tours, as is the more renowned Aintree course in Merseyside.

In the Midlands, visitors can take a Brother Cadfael Tour in Shrewsbury, visit George and Elizabeth Cadbury's house in Bournville (right), near Birmingham, or stroll around the Mill Garden in Warwick. Further north, in Northwich, Cheshire, the Grade 2-listed Anderton Boat Lift on the Trent and Mersey canal (the earliest Victorian boat lift) is worth a visit.

If you didn't go to Stowe, Harrow, Cheltenham Ladies College, Oxford or Cambridge University, now's your chance. All of these prestigious institutions have caught the weekend's glasnost spirit and are opening their doors. In Oxford, the William Morris-decorated Union and Radcliffe Observatory are highlights.

The range is extraordinary. Rochdale's magnificent Victorian Gothic town hall, the Grade I-listed West Pier in Brighton, a nuclear bunker in Dereham, Norfolk, the Ancient Chapel of Toxteth in Liverpool and BT's Directory Assistance centre in Northants...all these diverse places are wide open.

If your architectural appetite has been whetted, more than 400 buildings are also available for inspection in London next weekend. A back-stage tour of the Hackney Empire, a hushed trip around the 250-year-old Marx Memorial Library in Clerkenwell and entrance to the Ismaili Centre in South Kensington are all on offer.

So what's stopping you? It's a chance to find out where you've been living all these years.

A copy of the directory listing all the properties open this weekend is available from Tourist Information Centres (free), major reference libraries and comes free with the September edition of Country Living magazine. The directory of buildings in next weekend's `Open House' in London can be obtained by sending an SAE (39p A5) and pounds l in stamps to: London Open House, PO Box 6984, London N6 6PY

Peter Conchie