Why is Chernobyl so famous?

Answer 1

Because the world's worst nuclear reactor accident happened there. The reactor involved (a Soviet designed RBMK graphite moderated reactor) had many serious safety related design flaws, had been built in a rush to meet schedule deadlines without first having completed all safety related testing, and was undergoing a poorly planned and not properly reviewed test under the control of people with no knowledge of nuclear reactor principles (the man in charge of the test was only trained in hydroelectric dam principles).

This was a setting for disaster and disaster was what they got. Skipping over the details: the reactor became unstable and impossible to control during the test, it experienced a sudden power surge, a steam explosion resulted which blasted the roof off the reactor building (no containment building existed in RBMKs), with hot graphite exposed to air the graphite ignited, the smoke from the graphite fire carried radioactive debris from the damaged core across Europe and eventually around the world. Hundreds of firefighters died of radiation poisoning from the exposure they got in trying to extinguish the burning graphite and other fires nearby that had been started by chunks of burning graphite thrown from the reactor in the blast.

The surrounding land is slowly reverting to nature and has become a wildlife preserve, protected from human intrusion by the radioactivity.