THE past is opening up to the public this weekend as part of this year’s Heritage Open Days.

Tomorrow and Sunday will see many buildings in north Essex, which are not normally accessible to the public, open to visitors for free.

Colchester Castle will be opening its doors tomorrow from 10am until 4.30pm, while at Tymperleys Clock Museum, in Trinity Street, there will be a rare opportunity to view the upstairs rooms of the Tudor house, which once belonged to Queen Elizabeth I’s physician, William Gilberd. It is open from 10am until 1pm and 2pm until 5pm tomorrow.

New this year, is a special vintage bus service, which departs from the War Memorial, in Colchester High Street, either to King Edward Quay at the Hythe – stopping at Bourne Mill and St Leonard’s Church every half hour from 9.45am to 4.15pm – or to the Hythe and Essex University, hourly from 1.30pm to 3.30pm.

Open days this year include: * Colchester Royal Grammar School, Lexden Road Open tomorrow, 10am to noon. Talks at 10.20am, 10.50am and 11.30am. A chance to see inside the historic school, including the library, with its Jacobean fireplace. * Tours of the private rooms of Colchester Town Hall, High Street Tomorrow and Sunday, 10am, 11.30am and 1pm. The town hall was designed by Victorian architect John Belcher, and has its famous tower, topped by a bronze figure of St Helena. There will be tours of the courts and the mayoral suite. * Bourne Mill, Bourne Road Tomorrow, 10am to 5pm and Sunday, 1pm to 5pm. Bourne Mill is a 16th-century fishing lodge, which was converted into a watermill in the 19th century and is now run by the National Trust. The open days include music, dance and Shakespeare. * Audley Chapel, St Michael and All Angels, Berechurch Hall Road, Colchester Tomorrow, 10am to 4pm and Sunday, 2pm to 5pm. The 16th-century burial chapel of the Audley family, with fine hammer-beam roof, distinctive monuments and other features. * The Treadwheel Crane,St Helen’s Green, Harwich Tomorrow and Sunday, 10am to 4pm. This is the only British example of a two-wheeled, man-operated treadwheel crane, built in 1667 at a cost of £392, when Harwich had a Royal Navy yard. * Peake’s House, East Stockwell Street, Colchester Tomorrow and Sunday, 11am to 4.45pm. A timber-framed house, which was originally three buildings, some of which dates back to the late 14th century. * St Martin's Church, West Stockwell Street, Colchester Tomorrow, 10am to 1pm, and Sunday, 10am to 5pm. This is a medieval church with an impressive 14th-century roof, wall painting and a Norman tower, which was badly damaged during the 1648 Siege of Colchester. * Mercury Theatre, Colchester, Tomorrow, 10am to 2pm. Entrance by tour only, which takes place every 15 minutes. 01206 573948. A chance to take a backstage tour of this wonderful theatre. Built in 1972, it has been hosting some of the country’s biggest names ever since. *Vintage Bus Display, King Edward Quay, Hythe Tomorrow, 9.45am to 4.45pm. The Eastern National Vehicle Owners Club show a display of former Eastern National buses. There will be around ten vehicles, of which three will be in use, and seven on display at the Hythe. * Braxted Park Estate, near Witham Sunday, tours at noon and 3pm. Braxted Park dates back to the mid-14th century when it had a deer park. Pre-booking for the tours is required, on 01621 856503. * St James the Great Church, East Hill, Colchester Tomorrow, 9am to 5pm. Dating from the 12th/13th century and restored in the late 19th century this church features 18th and 19th century paintings, 17th century brasses, and the original organ from St Nicholas’ Church on the High Street. * Harwich Electric Palace, Kings Quay Street, Harwich Tomorrow and Sunday, 10am to 2pm. One of the oldest purpose-built cinemas to survive, complete with its silent screen, original projection room and frontage. Over the weekend there will be presentations on the history of the Electric Palace, the screening of classic cartoons and a craft fair. * University of Essex Latin American Art Collection, Essex University Tomorrow. Tours from North Towers bus stop at 11am, noon, 1pm, 2pm and 3pm, which lasts about half an hour. Take a guided tour of the university’s world-renowned collection of Latin American Art. The tour includes the library and the Hexagon – an iconic building soon to be a Museum of Latin American Art. * Colne Valley Postal History Museum, Head Street, Halstead Tomorrow and Sunday, 10am to 4.30pm. The independent postal museum is set in a suburban garden, with a display of more than 100 British post boxes, uniforms, bikes and postal equipment.