The oldest architectural monument in the Slovenian municipality of Moravske Toplice is a rotunda from the middle of the 13th century, dedicated to St. Nicholas. Its origin is still not entirely clear today, tradition mentions a connection with the Knights Templar.
The semicircular apse, window openings, portal, articulation of the outer wall and interior design follow the Romanesque style. With its image and method of construction, it is unique in Slovenia.
The interior is round, covered with a dome, the lower part of the cylindrical walls is divided by semicircular wall niches, which served as seats. The altar part in the semicircular apse is arched and illuminated by light penetrating through the window. The ground was originally made of compacted earth. The interior is painted with frescoes. The frescoes were subjected to conservation restoration between 1978 and 1980.