For minor injuries and illness, go to the local "Legevakt". This is an emergency room where physicians see patients without an appointment. The wait may be several hours.
Norway has a low crime rate with most crimes limited to theft and vandalism. As the largest city and capital, Oslo has a higher crime rate than the rest of the country, but it is still low. There are very few areas of Oslo that should be avoided after dark, but there are a few:
pedestrian stroll along the Akerselva river and around Grafanland
area around the street Skippergata
area above the Central train station
area around Majorstuen T-bane station
There is a red light district from Karl Johan's street to the harbour. Prostitution is legal, but a bit complicated as purchasing services from prostitutes is a crime. Also beware as this area can be seedy.
Norway has a unified police force, or politi. In rural areas police officers are called lensmann. Police officers do not usually carry guns.
Warnings signs are rare as most Norwegians expect people to watch out for themselves. Where there are warnings, pay attention.