It is a romantic garden that embraces the former thermal hospital, built under the ruling of D. João V. This was mainly a place for health recovery, where the patients of the thermal hospital could walk around and enjoy the soothing effect of the park.
However, in the end of the 19th century with the rise of bourgeoisie and the railway connection, the architect Berquó took charge of the thermal hospital and the park changed radically. It became a truly leisure area that included a central artificial lake, beautiful alleys, a music bandstand and police surveillance, attracting many visitors from the whole country.
Remodeled in 1950, Park D. Carlos I  was enlarged, including José Malhoa Museum and a restaurant.
It is nowadays a must-see spot of the enchanting city of Caldas da Rainha, along with the colourful fruit market and the Bordallo Pinheiro ceramics route.