I think we know a few of the most radioactive places on earth, but there are several others that never made the news. I spent several years in South America and I remember in the mid 80's-early 90's, several "ghost ships" (mostly Eastern European), dropping their anchors 25-50 miles off the coast of poor countries at the time such as Ecuador or Peru. They would send a small boat with a few crew members and a bag of cash, to bribe the major and authorities of small villages (and islands) in order to dump "waste". The authorities would take the bribes 99% of the time and then the big ship would "unload" its waste all over the coast (beaches, hills, etc).
These areas would eventually become ghost towns due to acute radiation syndrome, Cancer, mortality rates, infertility etc. Sad but true.