A controversial accommodation centre for families facing removal from the UK has been hailed as "excellent" and "groundbreaking" in an inspection report.
But watchdogs also described Cedars - which is set to close - as "little used".
Figures show 45 families were held at the facility near Gatwick Airport over two years since 2014, with just 16 subsequently removed from the country. Other detentions "failed" following legal challenges, "non-compliance and disruption" or other reasons.
Last month the Government announced that Cedars would be replaced with a more "cost-effective" unit following criticism it was underused and too expensive.
Previously described as "palatial", last year the centre was forecast to cost the Home Office £6.4 million. It features a gym and all-weather football pitch while there are games consoles for children.
Inspectors visited the facility in April this year and found that it had "maintained the high standards for which it has become renowned".
A report of the findings published on Thursday by HM Inspectorate of Prisons (HMIP) said it was awarded the "highest grades in all areas".
Referring to the announcement of its closure, Chief Inspector of Prisons Peter Clarke said: "The groundbreaking facility at Cedars will thus be lost, despite the significant human and financial investment in its success over the past few years.
"Cedars produced the best outcomes for detainees that we have seen anywhere in immigration detention."
Cedars was opened in 2011 to hold families who were subject to immigration control ahead of their removal from the UK.
Contained in a former school building, which is "essentially an extended Edwardian house set in extensive grounds", it consists of nine apartments ranging in size from one to three bedrooms.
The HMIP report said the whole facility had been "fitted out to very high standards", saying: "The grounds have play equipment, seating and sufficient space for families to take exercise and relax."
Cedars was said to have "gained an international reputation for the quality of its facilities".
The house has a fitness room, library and IT rooms, chapel, play room and lounge areas.
"The physical environment remained excellent and had in some respects improved," the report said.
There were nine "well-equipped, comfortable and spacious" self-contained apartments, while the centre was "well decorated with interesting murals and artworks painted on the walls".
Children and young people benefited from "stimulating and informative sessions" which helped them learn about the culture of the country they were going to.
Outside there are two adventure play areas, an all-weather quarter-size football pitch, and "landscaped lawns" with a "sensory garden".
Indoor facilities were "excellent", the report said, adding: "Older children could use a youth lounge with a television, up-to-date games consoles, table-football, snooker and a wide range of string and percussion instruments."
A small gym at the centre was said to be a "good training resource", while the library provided a wide range of English and multilingual books, DVDs, magazines and newspapers.
The report also described how detainees were provided with a mobile phone on arrival to "help maintain telephone contact with family, friends and legal representatives".
The average length of detention at Cedars was 65 hours and 55 minutes, or nearly three days.
Cedars is managed by G4S, the Home Office and Barnardo's, which provides social work, welfare and family support services.
Jerry Petherick, of G4S, said: "Today's report recognises the committed and dedicated work of our team alongside partners from Barnardo's and the Home Office and we can be rightly proud of the way we have worked together over the past five years for the benefit of those in our care."
The Home Office said the low level of use of Cedars is a testament to the overall success of the family returns process and the fact more families are accepting voluntary assistance to leave the UK when they no longer have a lawful basis to stay.
A spokeswoman for the department said: "We welcome the Chief Inspectorate of Prisons' findings and are clear that the welfare and safeguarding of children will remain at the heart of the family returns process.
"Stephen Shaw's independent review into the welfare of vulnerable people in detention recommended that we should draw up plans either to close Cedars or to change its use on value-for-money grounds.
"We accepted this and will be replacing Cedars with alternative pre-departure accommodation that will continue to safeguard and promote the welfare of children."