Underground karst water is accessible only in two caves near Logatec town (30 km south of Ljubljana, central Slovenia); Gradišnica and Gašpinova jama caves. Water level and water temperature were continuously measured more than one year in both caves. Gradišnica and Gašpinova jama caves belong to the same karst aquifer, therefore fluctuations of water level are almost identical and simultaneous.According to our measurements,fluctuations are significant;they rach at least 50 m.Incontrast,water temperature is significantly different at both locations.Mean difference is 1-2 °C, the highest measured was 5 °C. Relatively high temperature differences are due to recharge characteristics of the aquifer. It is fed by waters which have different surface origin. Water temperature in Gradišnica Cave directly reflects temperatureof the surface Unica River at medium water condition. On the contrary, the Unica River influences on water temperature in Gašpinova jama Cave at the highest floods only.Ithappens when discharge of the surface Unica River at Haasberg exceeds 40 m3/s. Water temperature becomes similarin larger part of the aquifer between both discussed caves, at such high water conditions only. Temperature of underground water tells us much about the origin of the water, which feeds discussed caves.