[Please see my reply below this original.] Caves are very rare formation usually found in mountains. They are vary rare as they are formed exclusively from a very unique creature that was found on earth in the jerassic period. The creature is called the secallius lumosur. This translate to giant worm. It lived most of its life underground, only coming into the outside world to mate. Caves can be found in very few places these days due to collapses and the extinction of the giant worm. They can be found in Germany and Russia.

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Caves are very common formations.

Yes they are found in mountainous areas but not exclusively so: they need limestone uplands but the relief need not be ever so high.

They do not have biological origins although their host lilestone may be highly fossiliferous.

That limestone may well be Jurassic (not "Jerassic") but could also be Carboniferous or Cretaceous: most of the UK' caves are in CarboniferousLimestone though some are in late Jurassic rock. Most French caves are in Jurassic and Cretaceous Limestones.

I've no idea where you found yourSecallius Lumosurbut it looks made-up.

What can be found in Germany and Russia?The worm or the cave?Both countries have caves - so does the UK, USA, China, Iran and many other countries.

Right - the serious answer to the question itself, as I assume the questioner wanted;
Most caves are in limestone uplands offeringsuitable geological, hydrological and long-term climatic conditions to encourage cave development,which proceeds by rain-water sinking into the rock's joints and other fractures and slowly dissolving it.

it is a person who explores caves.

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Not according to most such people.

I've no idea where the word originated [but now see below] - USA slang yes, but how, when & why I do not know. No American caving literature I've ever read, uses the word. The proper, international, term in the English language is "caver". Simple as that.

!!!

Since writing that below my '+++' answer-partition I learnt that "spelunker" was a rather pretentious but harmless invention by two American cavers in the 1930s. It was used for a while quite innocently and picked up the Press and non-caving public. Eventually the word became one of derision among cavers themselves for novices and dilettantes, and so faded away from caving publications; but this development was not realised by non-cavers.

There is a fancy word, Speleologist - this describes a caver who studies scientifically the caves themselves (geology etc) and their contents (wildlife etc.). The first e should really be the ae dipthong character, but it is usually now emasculated to just e. Notably perhaps, one of the world's leading speleology learned-journals is called simply Cave and Karst Science.

Mammoth Cave

ADDED: Depends on how to defines largest; but Mammoth - Flint Ridge Caves system has certainly world's longest knowntotal of surveyed passage length, I believe now >400 miles.

Cave paintings are paintings on cave walls and ceilings, and the term is used especially for those dating to prehistoric times.

San Miguel, Bulacan

*correction it should be " Imbakan, Tanggapan,Ospital and Tambakan"