Cracks in the upper crust are the result of either local or regional tectonic stress. Such structural elements are conduits for fluids in the crust. In Pamukkale, hot water which is rich in calcium carbonate emerges from fissures. The hot water issuing from the fissures precipitates travertine both in the fissures and on the surface. As a result, a ridge, which is called fissure-ridge travertine, forms along the central fissure. Fissure-ridge travertines are lens-shaped at the surface. Since fissure-ridge travertines are of great tectonic significance, their surface characteristics have been studied in detail. However, the subsurface geometry of travertine ridges is not well known. GPR was used to examine the subsurface geometry of fissure-ridge travertine and the central fissure. GPR profiles were combined across the ridge to produce a three-dimensional (3D) subsurface image of the travertine mass. The 3D image showed that the thickness and width of the travertine mass are at a maximum near the centre of the ridge and they both decrease asymmetrically towards the ends. Perpendicular GPR slices across the central fissure showed that the thickness of the vertically banded fissure-travertine increases with depth. 3D modelling suggests that the lateral propagation of the central fissure is asymmetric.