Considering that this falls under the "holiday entitlement" section, why not call it a "health spa holiday"? Health spa holidays are relaxing breaks that also include a certain amount of treatment.

This is for those of you who are looking for a ***health spa holiday*** which includes a medical examination and supervision, therapy, treatments for a variety of illnesses, rehabilitation, weight loss, addiction - or simply complete relaxation to unwind from the day to day rat race.
http://www.poland4all.com/subject.cfm?id=11&category=9

Thermal spas mean not only therapy but also a moment to let go and take care of oneself and when you start your ***health spa holiday*** you are starting your trip to a healthy and relaxing break which rejuvenates mind and body.
http://www.comunecervia.it/turismo/docs/docs.asp?doc=terme-s...





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Note added at 14 hrs (2007-07-04 21:34:28 GMT)
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Perhaps my "health spa holiday" interpretation stems from the many years in Germany where I (rather enviously, I admit) heard people brag about being sent for weeks on a "Kur" to (force them? allow them?) to take a break from work (and lose some weight, cut back on their smoking, etc.). While they were there, many of them picked up a "Kurschatten" - a quick little (extra-marital?) fling to go along with all the other "treatments".

The German "Kur" has become an accepted part of the post-war social welfare system. Germans have a "spa entitlement" that allows them to go to a spa (on a doctor's orders - and paid for by the health insurance company) on a regular basis. This excerpt from at 1996 New York Times article says a lot about "Kurkultur":

"Outside the clinic where Mr. Ruhs, a 55-year-old technician in a food factory, is about to be unpeeled and hosed down by Theresia Doppelgatz, the nurse who wrapped him in the mud known as fango, Hedwig Wilming is taking a smoking break from her therapy, and she seems to agree.

"Mornings it's fango, evenings tango," said Mrs. Wilming, a 50-year-old nurse, getting a laugh from other people who, like her, wear bathrobes and track suits to undertake the travails of a four-week, state-financed spa treatment, known as a "health cure," that has come to stand in microcosm for one of the most ferocious debates in Germany as it gropes toward unfamiliar austerity.

The question, in essence, is this: can Germany's welfare state continue to afford not just routine health care but also a system whereby, on a doctor's prescription, Germans like Mr. Ruhs and Mrs. Wilming may take a free four-week spa treatment every three years?

In Bonn, just north of here, the Government's answer is no. And, among measures supposed to save some $33 billion in public spending, it has proposed that spa entitlements be reduced to three weeks every four years. The German Government reckons that by trimming spa care and some other smaller benefits, it will save about $5 billion a year.
http://query.nytimes.com/gst/fullpage.html?sec=health&res=9B...

Okay, I concede that the word "holiday" does not fit all "Kur" situations. Sometimes a "Kur" is hard work - especially following an operation. It's no picknick recovering from major back surgery, etc. But, in my opinion, the word "treatment" - although it's used in the above-cited article - somehow sounds too OFFICIALLY MEDICAL for many (but, admittedly, not all) of these state-sponsored wellness junkets.

Given the rampant abuse of the "Kur" system in the past, perhaps "a doctor's prescribed stay at a health spa" would be more appropriate?

Sorry, Simon, I know you only wanted a short translation of a three-letter German word! Who was the translator that said the English is always shorter than the German!??