Dwarves are very superstitious creatures, and rarely leave their mountain. This superstition stems from tales of the great Dwarven adventurer, Carreg Axewielder. He wandered the world, and experienced many things, he was attacked by walking trees, had the sky fall on his head, and fought great and terrible beasts. He found the entire experience to be enlightening, but found, on his return, that his story struck fear into the Dwarfs, who hid themselves in their mountains, refusing to come out incase the sky fell, or the trees attacked them.
Dwarves are not obsessed with mining, nor indeed with gold or any other mineral, though there is some folk-belief that this is the case. Dwarfen mountains often do produce a lot of gold, which to most dwarves is generally useless. They are trying to build a secure and strong shelter, so that when the sky does fall, they will not be crushed by it. They have a natural fear of any wood that they don't consider dead, and most mountains have a well-guarded room where wood is put to make sure it's dead before they use it to make handles and other items that can only, rationally, be made out of wood.
This does not mean that people have not meet dwarves. A township next to a dwarfen mountain will often be full of dwarves, but they have not, in their own minds truly left their mountain, because they did not go through the large main doors. The have left through smaller, hidden, back-doors, and as such are, in a sense, still in the mountain.
This does not stop some dwarves, like Axewielder, thinking that adventure sounds like a good idea. A Dwarves can leave at any time they like, but custom suggests that they leave on their Gift Day. Young Dwarves (that is, all dwarves who have not had their first Gift Day), can choose when they are ready for their first gift-day, and will join that years “Gifters”. Dwarven ages are then counted from this day. (Thus, a 2 year old dwarf could have already lived 40 years, though for those 40 years, he/she would still be considered a “young” dwarf). As is the custom on their first Gift Day, the new dwarves will celebrate their coming of age. All those who wish to leave (which are not many, on average less than 1 a year) will then celebrate their wake, in case they don't return from “Outside”. They will be made blind drunk, and when they pass out, they will be placed outside the gates, and the gates will be closed. This is in remembrance of what happened to Axeweilder (though he only stepped outside to relieve himself, and then passed out). The family and friends will often leave gifts that may be useful, axes, food, even maps (though maps are often very out of date, having been drawn by the last dwarf in the family to go “outside”, and return, which could have been generations ago). The dwarf will be considered legally dead until he returns. A Dwarf cannot return through the back doors, and if s/he tries, they will be treated as a stranger. To return, a dwarf must camp ouside the main doors until the next gift day and enter that way. Gift days are not held on the same day, as they are dependent on the organisers, the mining that is happening, and other celebrations. Gift days are always in the summer. A return dwarf could well find themselves camped outside for a long time.
Dwarfs are short, the tallest dwarf never growing more than 4ft 10”. They often have beards, and have a tendency to ware armour, and thick helmets (to protect themselves from the falling skies/attacking trees/other things they are afraid of). Unlike popular myth, female dwarves do not have beards, and are often well-endowed. Females dwarves who go “Outside”, however, are even rarer than the males, leading people to the popular belief that female dwarves have beards.
Dwarves tendency to be rather paranoid about the world being out to get them.