When I was a child, my mother taught me not to get into a car with a stranger.
When my car broke down, a kind stranger stopped to help me.
A foreigner is someone who comes from another country:
This town is a popular tourist destination, so there are always a lot of foreigners around.
The new law makes it easier for foreigners to get documents to work legally.
A lot of foreigners have been moving into this neighborhood - I've met people from seven different countries in my apartment building alone!
The word alien is a legal term for foreigner. It is usually used to describe "illegal aliens" (people who are in the country illegally) or "resident aliens" (people who are living in the country legally). Again, this is formal/legal language and in everyday speaking it's best to use foreigner.
Alien also refers to creatures from other planets; it is another word for extraterrestrial.
Sanqingshan is a relatively small National Park near the city of Shangrao in the Jiangxi province of China. What it lacks in size it makes up for in shear natural beauty. It is officially the 7th World Heritage Site designated in China and has been noted for its exceptional scenic attraction. The key mystique of this remarkable place is the combination of extraordinary granite geology in the form of weird outcrops and pillars combined with seasonal climate variations than often cause mists, fogs and striking sunsets. Those that have visited this place describe a feeling of overwhelming peace and tranquility. This effect is enhanced by the profusion of natural waterfalls, pools and springs. If you allow yourself, it is truly possible to see Earth, Water, Wind and Fire joined in time.