Green’s Dictionary of Slang

Holloway castle n.

also the Castle, royal palace of Holloway
[before its mid-20C+ remodelling the gateway of the original Holloway prison (now England’s main women’s prison) had ‘castellated’ architecture, copied in part from Caesar’s Tower, Warwick Castle; the pub across the road is still called the Holloway Castle]

Holloway prison.

[UK]Islington Gaz. 30 Dec. 2/5: An inquiry was held on Friday, before Dr Lankester, at ‘The Castle’.
[UK]Sporting Times 8 Nov. 2/4: ‘Drive uth up the Camden Road till you getth to ‘Olloway Castle’.
[Scot]Edinburgh Eve. News 20 June 4/6: ‘Holloway Castle’ A Debtor’s Prison [...] that delightful place Holloway Prison, or, as it is more familiarly known, ‘Castle’.
[UK]Sporting Times 1 Feb. 3/1: Though I had just received a pressing invitation from no less a personage than H—r M——y to spend six weeks or so at the royal palace of Holloway, I lost no time in [...] preparing for the journey. [Ibid.] 22 Mar. 6/5: Wm. Swillington Shifter, Esq., B.A., Holloway Castle, N.
[UK]Daily Tel. 20 Apr. in Ware (1909) 153/2: It may be taken as highly improbable that Her Grace (of Sutherland) will be subjected to the indignities which are alleged to have been suffered by persons who have purged their contempt of Court by terms of imprisonment at Holloway Castle, as the gaol is called.
[UK]Binstead & Wells Pink ’Un and Pelican 131: The alternative being a month or six weeks in the picturesque, old-world castle at the lower end of the Camden Road.
[UK]Portsmouth Eve. News 16 Dec. 3/5: The bank clerk Goudie, charged in connection wioth the Bank of Liverpool frauds, is confined in ‘A2’ ward of Holloway castle.
[UK]A. Binstead Pitcher in Paradise 12: It turned out to be a matter of £36.16s.8d. or Holloway Castle.
[UK]J. Curtis Gilt Kid 38: ‘I just came out of Holloway this morning.’ ‘Out of the Castle, eh?’.
[UK]P. Hoskins No Hiding Place! 192/2: The Castle. Holloway Prison.