LocalFluff: Yup, limestone or karst terrains do not correlate with mountains or valleys or any topology. They are formed from the sedimentary deposit of sealife underwater, over many eons. When the ocean recedes and the sedimentary layers are later crushed, shifted, deformed, and reshaped, they can be found in almost any terrain.

All that is really required is that at some point in past that karst was once at the bottom of an ocean or sea, for a long enough time to build up layers.

So karst is where the water could’ve made clear water reservoirs, or even streams by eroding soft rock (limestone). In contrast to the general water table that just saturates whatever mud or rock is down there?

The large scale world maps of karst geology formations don’t seem to have much relation to what’s on top of them on the surface. There seems to be one such formation beneath the Ural mountains, but nothing beneath the Andes, for example. And no apparent correlation between jungle or desert. Nor with tectonic plate boundaries. Nor with latitude.

Seems hard to figure out where on an exotic place like Titan there is potential for subsurface lakes.

LocalFluff: Be aware that cavers do not use the term “spelunker.” since to us it refers to someone who hasn’t the faintest idea what to do underground and almost always needs rescuing.

On Earth most caves are formed by water flowing underground through limestone. That limestone or karst geology has been well-mapped worldwide (do a search on DuckDuckGo), but on smaller scales is very incomplete. This is one reason why cavers explore, because the discovery of new cave passages helps map the underground drainage in karst terrain, since in that terrain almost no water flows on the surface. It all sinks.

Furthermore, all land masses on Earth have what is called a water table. At a certain depth (which varies) you will always find water underground. This is why people drill shafts for water.

For Mars they have labeled this the ice table, though the two are not entirely comparable.

Subsurface lakes and oceans have been proposed on multiple moons and Mars. On Earth I’ve heard of a lake under the ice on the Antarctic continent. How well is the occurrence of subsurface lakes and even rivers known on Earth? Is it hard to figure out, or are there even large regional maps of them?

It’s one thing in mountain chains with glaciers or seasonal snow melt, but I wonder about below the sea level, or even below the sea bottom.