From the point of view of the origin of the cave is divided into natural (karst, lava) and artificial (mining, mines, mines, quarries, salt mines).
The caves are very different. They are horizontal, vertical, and are divided into dry and watered, plain and labyrinth.
As a rule, the caves, both natural and artificial, attracted the attention of the opportunity to escape from the weather and predators and detect water. The main danger in the survey of caves is that they are very easy to get lost, even with their small extent, because the cave can be a maze, the failures that are difficult to see in low light the floor, the probability of landslides. Finally, the worst — can suddenly be left without coverage in the fall or a sudden breeze that can extinguish torch, homemade beeswax candle or fat lamp. Therefore should be removed from the entrance only within the penetration of sunlight into the cave.
Any examination of the underground cavity alone is fraught with great danger to life. But if you still have this urgent need, then:
must have sufficient lighting and, importantly, the ability to quickly extinguished torch to light a candle or something else;
go slowly, constantly illuminating the walls, ceiling and floor in time to detect falls, failures in the cave floor, side branches;
in the presence of branches required to mark the direction of the exit;
never try to go that one, then another branch and follow the rule of "right hand", that is to go deeper, keeping only all the right moves, and back — and all left, or (preferably) to return the same way, remember that all incrustations in karst caves quite brittle, so use them as a serious support for gradients can, in mines old wooden fasteners can be rotten and extremely unreliable and can cause a collapse of the roof even with a light touch;
in some, both natural and man-made underground cavities can have a different gas. In some cases, it puts out an open flame, your light source, in other — there is an odor. In both cases, you must immediately leave the cave or output.