The original name for Hotel Koldingfjord was "Julemærkesanatoriet", meaning “The Christmas Seals Sanatorium” because it was the first of a series of sanatoriums built with money raised from the sale of Christmas Seals. In 1904, Einar Holbøll, a Danish postal clerk, developed the idea of adding a charitable stamp on the postage of Christmas greetings cards, with the money raised going towards helping children with tuberculosis. The plan was approved by the Postmaster General and King Christian IX of Denmark and Hotel Koldingfjord became the first Christmas Seal Sanatorium to be built in Denmark.
Sales of Christmas Seals started in 1904 and raised 67,000 krone, the equivalent of around $1.5 million today. It was decided that the money should be used for the construction of a sanatorium for children affected by pulmonary tuberculosis, and after much debate, an area, called Louisehøj, on the banks of Kolding Fjord, with adjacent hills, was purchased.
Julemærkesanatoriet was built between 1907 and 1911 and even though the construction was budgeted at DKK 600,000, the final cost was DKK 1 million. This was mostly due to extensive problems with the foundations, which were too soft. A stable foundation had to be created by using end bearing piles. This meant that engineers drove piles of timber deep into the ground to support the structure and prevent the construction from slipping into the fjord. It is said that there is just as much underground as above ground!
From 1911 to 1960, the building served as a sanatorium for children affected by tuberculosis and was an important element in the fight against a major public health threat.
During the last 100 years, the building has had a variety of different functions. For example, where the terrace is today, there was once an outdoor lounge. The Conference Halls were previously a kitchen, a dining room for the children and the staff and areas for medical ultra-violet light baths. The reception area was a large living room, off the corridors there were medical rooms, x-ray areas and large wards. On the first floor there were small bedrooms in the middle, and wards on each side. The top floor consisted of an operating room and dental clinic in the centre and wards on either side. The building behind the main building, where the conference rooms, Magnolie and Bøgesalen are today, was originally the gymnasium and boiler house, while the side buildings, now called Dagmar's Palæ and Christian's Palæ, were used as a school and offices.
After 1960, tuberculosis had been eliminated in Denmark and the buildings were taken over by the County’s Department of Mental Health Services to be used as a children's psychiatric facility. This closed in 1983 and the building lay empty until, in 1987, the Danish Nurses' Organisation took over the property and charged architects, Vilhelm Lauritsen and Jørgen Stærmose, with renovating the beautiful Rococo and Renaissance inspired building to create a modern hotel and conference centre.
Between 1988 to 1990, the listed buildings were extensively renovated and inside, the property underwent a complete renovation and modernisation and was equipped with the latest facilities for a modern hotel and conference centre.
On 1st May 1990, the property opened under the name Hotel Koldingfjord.