I was surprised to discover that there is a gateway to hell in Stull, Kansas. Although that would explain all of Kansas history from Quantrill's Raiders to Sam Brownback.
According to legend (or maybe the bible or Quran) there are seven (or six) portals to hell located on Earth. According to the internet the planet is pockmarked with dozens of entrances to the devil's domain with an inordinate number in the US alone. Excluding Stull, here are my seven choices.
New Jersey Sewer
Lake Avernus, Italy