Recent observations have shown in some sunspots the presence of structures that have been called umbral filaments (UFs). These consist of bright filamentary features intruding sunspot umbrae, different in morphology, evolution, and magnetic configuration from usually observed light bridges. We report on the properties of an UF observed inside the umbra of the giant leading sunspot in active region NOAA 12529. We analysed high-resolution observations taken in the photosphere with the spectropolarimeter aboard the Hinode satellite and in the upper chromosphere and transition region with the IRIS telescope. These observations were complemented with data from the Solar Dynamic Observatory satellite and from the INAF-OACT equatorial spar to study the evolution of this structure. We find that the UF harbours a strong horizontal component of the magnetic field and a portion with polarity opposite with respect to that of the umbra. In the upper atmospheric layers, the structure is cospatial to a bundle of filaments, which appears to be rooted in the sunspot umbra. We propose that the UF is the photospheric counterpart of a flux rope touching the sunspot and giving rise to penumbral-like filaments in the umbra via magneto-convection.