You're probably thinking of the aftermath of a nuclear weapon detonation, a power plant meltdown, or at least, a calamity of some sort. Interestingly enough, one of the most radiation heavy zones in the world happens to be a quaint little town in Kerala. A town that has been continuously bombarded with exponential amounts of natural radiation than what is considered healthy.

Some researchers claim that background radiation is a kind of inherently present ionizing radiation, the origin of which is a result of the Big Bang.

While it can be a result of natural or artificial causes, it is everywhere. Cosmic microwave radiation, naturally occurring minerals and nuclear fallout are some of the scenarios serving as causes. There is a persistent and constant natural background microwave radiation that runs through the universe in varying amounts in any case. But certain pockets on our planet serve as havens for increasing radiations levels.  

Source: en.wikipedia.org

Karunagappally in Kerala has been suffering a constant wave of high radiation exposure.

Certain international standards would rate not more than 5 milligrays per year as the allowable limit, beyond which radiation exposure may begin to take harmful affect with prolonged exposure. Karunagappally, as The Hindu reported in 2011, witnessed researchers observing the radiation levels in 12 Panchayats go up from 0.32 to over 76 milligrays per year.

Source: datab.us

The cause for the high background radiation are minerals in the soil surrounding the area.

More specifically, monazite present in the soil can contain between 8 to 10.5% traces of radioactive Thorium. The harvesting of metals from the soil has been the primary reason behind the effective spread of the radiation zone. 

While studies claim that the cancer and leukaemia cases reported within the municipality have little to no correlation with the background radiation levels, its harmful effects are far from trivial enough to ignore. At high levels, background radiation has increased the frequency of chromosome aberrations in the circulating lymphocytes of exposed persons in the past.      

One of the highest natural radiation levels ever recorded.