Green’s Dictionary of Slang

Castieau’s hotel n.

(Aus.) a prison.

1859		Ovens & Murray Advertiser (Beechworth) 10 Aug. 3/3: [T]he Bench ordered her to pay a fine of 20s with 9s 6d costs, or in default to retire to Mr Castieau’s hotel for a period of 24 hours.
1869		West Bourke & South Grant Guardian (Bacchus Marsh) 26 June 2/3: She [...] was arrested at Pentridge, tried and committed at Williamstown, and is now enjoying the comforts of Castieau’s hotel (late Wintles) .
1876		Ballarat Star (Vic) 1 May 2/6: For a long time he languished in the limited atmosphere of Mr Castieau’s s hotel, but a judge of the Supreme Court has opened its doors to him, and a [...] he will no doubt change his lodgings in the course of the evening.
1889		D. Sladen in Barrère & Leland Dict. Sl., Jargon & Cant I 229/2: Castieau’s hotel (Australian thieves’ patter), the Melbourne jail, so called from Mr. J. B. Castieau, the governor of the Melbourne jail.
1922		Labor Call (Melbourne) 8 June 2/1: The first governor was Wintle, and the gaol became facetiously known as Wintle’s Hotel. His successor was Castieau, and Castieau’s Hotel became the popular name for the institution.
1999		(ref. to late 19C) M. McKay On Tap 16: [W]hen Ned [Kelly] was hanged, it was at ‘Castieau’s Hotel’, the slang name for Melbourne Gaol, after the gaol’s Governor, J. B. Castieau.