It depends how you think about dangerous!
Danger from humans could either be in an area with a high mortality rate or a war zone. Danger from the elements and other factors could come in many ways:
1) Heat; unprotected you would not last long in Death Valley, which was recognized in September 2012 as being the hottest place on earth at a staggering 56.7 degrees Celcius (that's 135.68 fahrenheit)
2) Cold; Survival time would be very short at Vostok Research Station in Antarctica on July 21, 1983. The temperature was measured at -89.2 degrees C (-128.6 F).
3) Pressure; at the bottom of the deepest water on earth the Marianas Trench the water pressure is 15,750 psi, over one thousand time the pressure of air at sea level.
4) Lack of oxygen; at the top of Mount Everest, the oxygen is only around 30% of the density at sea level. Climbers must acclimatize themselves to be able to breathe without apparatus. If you went directly from sea level to the peak you would be asphyxiated.
5) Lava; most of the earth is made of molten rock, or lava, this is so hot that if you fell into it all of the water in your body would almost instantly turn to gas causing a small exposion.
6) War zones; never a good place for a long and happy life, despite the reduction of the number of people required to fight nowadays, if you are one of them - or an innocent bystander in the wrong place at the right time - death could easily ensue.
7) Insects, it has recently been shown that the humble mosquito has caused more deaths than any other cause - simply by transferring deadly diseases from person to person. The tiny Mosquito delayed, and nearly stopped the building of the Panama canal! En.wikipedia.org/wiki/Panama_canal
8) Animals, Lions, Tigers, Alligators, Sharks, Bears, these animals and many more can be a danger to us, either because we scare them so they attack us or they want to eat us - go to where they live and annoy them for a short life.
9) Homicide; it can seem worrying that some areas have such high murder rates, and not something that should attract you to these areas. But the truth is most homicides are not random, but are, gang or family based. Most people are essentially kind and will be charming and helpful if asked for assistance.