Is this a run-on sentence?
At Okunoin, Japan's largest cemetery, visitors will find some unusual memorials, there's even a monument to puffer fish that have died at the hands of chefs.

 - no
 - yes
This is a run-on sentence. It is a comma splice formed from two sentences run together, joined by just a comma.
At Okunoin, Japan's largest cemetery, visitors will find some unusual memorials, there's even a monument to puffer fish that have died at the hands of chefs.
Here is one way to fix the run-on sentence:
At Okunoin, Japan's largest cemetery, visitors will find some unusual memorials; there's even a monument to puffer fish that have died at the hands of chefs.