I am not sure I would recommend this hotel. The spa facilities are very good, there is everything for a wonderful weekend of all sorts of fitness / thermal pool / hammam / massage / jacuzzi / sauna / any wellness stuff imaginable. But that is the spa. And the spa is ndependent of the hotel itself. The only (great) advantage of this hotel is that it is internally connected to the spa facilities, so you can walk in your bathrobe from your room to the spa. As a hotel, the standard rooms are old and worn, definitely not up to the 4-star standard. There is wifi, but not complimentary (a "PT hotspot" which requires a prepaid card). With your room you have free access to all the basic spa amenities for the entire day (this includes checkout day, all day). But I think you get the same in the smaller attached hotel "Welcome", a 3-star facility, run by the same reception desk, which is obviously cheaper and only 50 meters away. The only disadvantage is that you would enter the spa from outside. Although I have not seen the "Welcome", I would find it hard to believe that it is not a better value.
As for Mondorf itself, I don't think there is much to do apart from the spa and perhaps a walk around in the park or in the nearby countryside. You really come here for the spa.

The Mondorf Parc is an unusual venue for a business meeting, but it turned out to be a winner. Arriving in the morning with no room available, the front desk offered a robe and a towel and immediate access to the spa. Nothing could have better relieved the strain of an all night flight than a collapse into the thermal pool, followed by a short nap in the comfy reclining chairs around the edge. Moving on to the large (and nearly empty) sweet water pool and the sauna village was equally stress-relieving.

Once the room opened up, it turned out to be a roomy suite in the taller wing. I'm not sure I've ever slept so well -- mineral baths, fresh, fresh air, fitness training and then comfortably simple beds. The hotel itself has a cavernous concrete motif, which does contrast with the delightful gardens, and classy older section with trendy cafe.

Mondorf was an unexpected treat. It is not near anything else you're likely to plan to visit, but as a conference site in the middle of Europe, I can't imagine a more charming option, a world of its own.

The big bonus to staying in the Domaine Thermal hotels is free access to the thermal pools and spa facilities. Based on the brochure offered by the spa, I did not think the spa treatments, compared to other spas I've visited, were overpriced, and though I did not get to try any of the treatments since our time at Mondorf-les-Bains was limited to one night and the following morning, I would really like to try a spa/hotel package the next time my husband and I visit.

The hotel staff were very helpful in finding us an excellent babysitter for the evening of our stay, and the thermal pool facilites are great! We had a fantastic time swimming, hot-tubbing, etc. there. We also dined at an Italian restaurant just steps from the hotel (the hotel's restaurants all close at 9:30 p.m., which would be my one complaint; I wish they kept at least one of them open 'til 10:30 or 11 p.m., since the thermal baths close at 10 p.m.), and it was very good.

Regarding our hotel room, it was sizable and the bed and bedding were very comfortable. We were able to have our small dog stay with us, and there was plenty of room for our baby's cot (in fact, our room had a sort-of antechamber where she was able to sleep, which made staying at this hotel all the more comfortable).

The town of Mondorf-les-Bains is small, very clean, and charmingly historical. I was sorry we did not make it to the casino, but will relate that the Domaine Thermal hotel offers a coupon for free admission to, and a free cocktail at, the casino (at least they were doing so during our stay, keeping in mind, however, that we were there mid-week).

I definitely recommend both the Domaine Thermal hotels and a trip to Mondorf-les-Bains in general!

I have stayed here twice, on both occasions on business trips.

First visit
Excellent / superb / brilliant ( add your own superlative ! )
Great spa and thermals, lovelly room. Bar is a bit pricey.

Second visit
Very average
No bar service for meals, restaurant was closed ( only 8:30 pm ! )
Nasty room in the annexe 500 meters away.

If you stay.... get there early, make sure you get a room in the main hotel.

ENJOY THE THERMAL SPA !