Visitors to the mill, which has roots going back to 974, will be able to learn about how grain passed through the building and the various processes involved in turning it into flour.Steve Bellis, visitor experience manager at the National Trust property, said: We have got a team of three volunteers who jumped at the idea of doing the guided tours. They are all very passionate about the mill and about how the building was managed. The tours, for groups of 10-12 people, will take place at noon and 2.30pm on Mondays and Thursdays between July 23 and August 23 and could become a more regular feature if they prove popular. Visitors will start outside the mill where they will be told about its external features before moving inside to see the machinery which is still used regularly to mill flour. Mr Bellis said: It is not so much about explaining the significance of the building, it is more about what happened inside. Once people come into the building they will follow the milling process we have in the building and follow the grain through the building. Houghton mill is the oldest working water mill on the River Great Ouse which once boasted 121 over 70 miles of river, including up to six between Godmanchester and St Ives. Boats used the river network to transport its produce to London and further afield. The mill was once part of Ramsey Abbey where records date it to 974 - although the building which stood there then could have been even older, and once belonged to King Henry VIII before being sold by Charles II. The present mill was rebuilt in the 1750s - with some of its equipment remaining from the period - with additions in the 19th and 20th centuries. Mr Bellis said the repeal of the corn laws in 1846, which put tariffs on imported corn, was the death knell for many traditional mills since it meant mills were set up at ports. Food additive regulations in 1916 meant other mills went over to making animal feed. Houghton Mill closed in 1928 and was bought by residents who handed it to the National Trust but it was run as a youth hostel until the 1980s when the trust took it on. Places on the tours can be booked on 01480 301494 and non-National Trust members have to be the standard entry fee.