In 1929 the use of a large part of the Castle Precinct as a gaol or military detention centre ended. In 1934 the prison buildings and five acres of land were purchased by the City from the Yorkshire County Committee (of the Three Ridings), who administered the area of the Castle. The Yorkshire Committee offered the land to the City at a fraction of its market value because, as the City explained in its application to the Ministry of Health to purchase the land
"they were anxious that this historic site should not come into the hands of an individual or company who would utilize it for profit, irrespective of its amenities".

In 1935 the gatehouse and all buildings later than 1824 were demolished. These included the Governor's House, a characterful circular building, and the gatehouse, which contained a records office, holding cells and a courtroom. The 35ft high wall was demolished or reduced to a token presence. For a time it was left several feet high between Clifford's Tower and the Foss, along the Precinct's northern boundary. The footings of the wall along the Foss were retained to shore the bank and in anticipation of a proposed riverside walkway. Aerial photographs taken in 1928 and 1947[1951?] show the extent of the changes.

Demolition of at least part of the prison wall had been debated for fifty years. In 1890 the County Committee was petitioned to retain them: "The walls proposed to be removed are of most perfect workmanship and mark an era when Yorkshiremen were able and willing to build in something better than brick stucco. In these respects they are unique in the kingdom, and thus form a national monument, of which any city might be proud to have the custody. They are provided with handsome buttresses and battlements which form one of the most pleasing features in the picturesque view of the Castle from Skeldergate Bridge."

In 1908 the issue was raised again, and in 1909 Coun.Oscar Rowntree moved a resolution that the Town Clerk should write to interested authorities. It was felt that removal of the wall would enable "the slope of the mound to be visible to give an idea of the original contour of the mound and add to the amenities of the pleasant neighbourhood of St.George's Field and riverside."

In 1913 notice was give that: "The Estates Committe of the York Corporation recommend the Council to seek power in the [York Corporation] Bill to be promoted in the next session of Parliament to advertise the attraction of the City and to remove the walls round York Castle." The County Committee at its quarterly meeting on December 30th 1913 received a deputation from York City Council Council and the Yorkshire Philosophical Society explaining and advocating the removal of the part of the walls between the gatehouse and the Assize Court along Tower Street, to widen it at some time in the future for electric trams. The Yorkshire Committee, however, feared that removal might result in the loss of the assizes, and successfully opposed this part of the Bill.

By 1935 the walls had fewer defenders, though there was a lobby to preserve the gatehouse [left, in the picture below]: "for more than a hundred years nothing has been built in York which can equal this gateway either in architecture, work or dignity". Between August - November 1935, the walls came down. A recent book on York recalls that crowds came at the time of demolition to marvel at the buildings they had never seen. In fact, there was public access through the gatehouse to the Assize Courts and to Clifford's Tower. The 1928 photo shows two tennis courts on the Eye of Yorkshire. The wall which restricted access to the southern part of the site is shown on the left. A wall, 20ft high, also encircled Clifford's Tower, whose mound had been cut back. The Office of Works restored the mound to something like its earlier extent, using stone from this and the outer walls, and from St.Mary's Abbey.

 The C19 gateway to Clifford's Tower at the 8 o'clock position in the left photo] lies beneath the mound today. The present steps were constructed in 1935. The 1950s photo, evidently taken during a prologed dry period, is revealing. It shows that all round the slope the join between the original mound and the new extension was not quite perfect. Nor is it now, in spite of the latest profiling! The outlines of the huge flying buttress of 1902 beneath the turf are faintly visible.

When the City first acquired the site there was an intention to demolish the two C18 prisons. These were saved by enlightened members of the Corporation, County Committee and learned societies, and by the timely intervention of the Commissioners of the Office of Works. The buildings became listed monuments - but it was a close call.

The Female Prison was extensively modified, the open exercise yards were roofed, and a path was made to it along the Foss. This was intended to continue as "a riverside boulevard to the ancient angle towers by Castle Mills Bridge". In 1938 the Female Prison was opened as the Castle Museum.

Next to it, foundations for a suite of health clinics and, to the north, municipal offices were laid from 1939 by Concrete Piling Ltd. at a cost of £19,275. These architect for these buildings was chosen by a competition which attracted 46 schemes.