Dungeon crawls are probably one of the best known and most beloved fantasy gaming activities, standing the test of time after decades of exploration. But are we really getting the most out of our underground experience?

One of the first things to wonder about is how common artificial underground complexes would be versus natural cave systems. I'm talking about dungeons: flagstoned floors, propped stone walls, torches flickering in sconces, ironbound oak doors securely sealed with sophisticated locking mechanisms.

In the real world, these are quite rare. In most fantasy worlds a wide variety of tunnelling races with varying degrees of skill could probably make the classical dungeon more common. That's without even thinking about evil wizards and tyrannical warlords who might spontaneously create labyrinths of well ventilated tunnels for our heroes to explore.

But why would a selection of tribal groups, random monsters and peculiar entities go to all the trouble of finding one of these somewhat rare single-entrance locations, assuming they're even empty, and occupying them when there are probably a far greater number of natural caves and caverns available?

This list of known and explored cave systems is enormous, and far from comprehensive, you could probably find a score of caves within a few days travel not on that list. Natural caves can vary from the size of vast cathedrals all the way down to crawlspaces stretching many hundreds of miles. They usually have many different entrances - some very well hidden, turning even the process of finding the entrance into an adventure - and are riddled with side tunnels, cracks and ways to get around without being seen.

Absolutely ideal for small bands of raiders or monsters to squeeze into and vanish with loot or captives!

Plus there's plenty of room for many diverse creatures in one location. Your group might be alerted to the presence of a cave system in the area if there are a lot of nocturnal raids from large monsters, so they might track some back to their lair, consult local legends and sages, or even employ magic to find the way in.

Such caves are also typically of immense antiquity, tens or hundreds of thousands of years old, so there could be both treasures and terrors raided or hidden from long forgotten kingdoms, magicians, and races in the depths. Some of this very ancient magic might even be put to use by the latest denizens of the caves. It's also a good opportunity to introduce new monsters or variant monsters from the deep and distant past.

So how would exploring these caverns differ from a normal dungeon crawl? The variety of environments would be the most important way, if characters weren't hunched over or crawling between two rock walls, they might be swinging over abysses or wading through icy, slippery streams. There's no imaginable layout that couldn't exist, and in three dimensions too, the main advantage of natural cave systems over regular dungeons. They lend themselves to all sorts of creative problem solving, swashbuckling, and derring-do!

The challenges presented by natural cave systems with added fantasy monsters are exciting - imagine battling goblin tribes up the slope of an underground hill with only a few feet above you, or through a series of vertical drop caverns dodging from outcrop to stalactite. Even low level monsters become a much more serious prospect when they've constructed simple booby traps along their rat runs!

Natural dangers - even without monsters -  would include tripping and falling down lethally deep drops due to dim torchlight on uneven muddy surfaces, gas pockets, bad air, getting lost in complex cave systems where mapping is almost impossible, rockfalls, hypothermia, getting stuck, especially in vertical pinches, and disease (animal droppings can bring fleas, unpleasant fungal infections and pollute groundwater). These are just a few of the hazards your group can pit their skills and creativity against without ever meeting a monster.

Caves usually come in four main types:

• Solution Caves are the most common type. This type of cave is formed very slowly by water in limestone or gypsum. The water actually dissolves the rock. As the passages get bigger and there is a faster water flow, water erosion becomes a factor. These are formed slowly and collapse rarely. Solution caves are scattered, in pockets, and have a wide variety of rock formations.
• Talus Caves are literally piles of boulders. They tend to be very confusing and are easy to get lost in. Also, the predominance of broken rock makes them very hard work. They tend to occur in mountainous areas, especially near cliffs made of a very strong rock, such as granite.
• Ice Caves are generally restricted to glacial areas. They are so cold that they could be dangerous. However, ice formations of extreme beauty and delicacy are often found.
• Volcanic or Lava Caves can be found near some volcanoes. They are passages which formed around and finally over flowing lava. Once insulated by the surrounding rock, the lava stayed hot enough to drain out when the eruption ceased, leaving a cave. These caves tend to be extremely jagged, and they can cut clothes to ribbons.

There's no reason why natural cave systems couldn't be combined with artificial underground chambers as well of course, or even passages created by burrowing monsters, but a GM can take good advantage of the force multiplying effects of narrow cracks to make smaller or weaker monsters much more interesting.

So make natural cave systems your go-to dungeons today and see how they work for you!