A large vertical cave has a constant, strong wind blowing out of it from the bowels of the earth. If one was to jump into the currents they would have a controlled ascent on the winds till they reached a height where their weight and the winds force reached equilibrium. Impossible to climb down naturally. What is it? Natural winds from the earth or a complex magical protection for an underground lair?
Mining in a certain area turns all exposed skin (maybe just parts that are actively disturbing the chemicals that cause the reaction) of the those doing the mining to a dark blue color. Will wear off taking as many years/days spent in the mine.
"Ladies and Gentlemen of Worth, please come closer and have a look... " In a little stand with numerous maps, the human Advantos sells land-rights with a shining smile and jovial talk at bargain prices. He sells even squatter rights (first to settle is the owner). About 20% of the lands do not exist or belong to someone else. About 30% do not have even that value, or have other problems attached- swampy, cursed, haunted, Old Indian/Pet Cemetery (tm)... Be assured you will not see this man in the same city twice.