The temperatures I'm hearing from the probes would not be conducive to water in the liquid state (unless pressure is very low). Also, probes have not mentioned any traces of humidity or water content in the tunnel "air". If there is standing water in the vicinity, it would be reasonable to assume that there would be an equilibrium with at least a trace of water vapor in the air.
Note: any appreciable humidity in a Carbon Dioxide atmosphere would be extremely conducive to corrosion in metal parts - you would have an essentially acidic condition. Humidity in an oxygen atmosphere just facilitates oxidative corrosion with metalic surfaces.
It's not a certainty, just a likelihood. If the ambient temp. conditions are elevated somehow (geothermal???), then it is possible to have a collection of water in such a cavern.
Now why would the Ipsos want to have their "party" in such a place?
Pool Volleyball, anyone?
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Zero
O=o