Constructed over 700 years ago Houska Castle in the Czech Republic is built over a chasm, which for centuries those who live in the area leads straight to Hell itself. Before anything else was on this spot, there was simply a massive hole in the ground and nearby villagers in Doksy, Czechia, who lived in terror of it. Accounts began to spread, 
that at night creatures would climb out of this mysterious pit, and there were winged creatures who would fly out and circle around. This kept the terrified residents in their homes once night fell. Over the years they made use of this, portal to hell by throwing criminals into it's depth as a form of execution. According to local lore, one curious young man during this era took it upon himself to explore what was in the mysterious hole. Lowered down by a rope, he made it just out of sight, until something terrified him and he was quickly brought back up. According to witnesses he had aged multiple decades in the span of a few moments.
Eventually the tales of demonic creatures terrorizing Doksy made it up the ladder, and Ottokar II of Bohemia decided something had to be done about it. In 1253 construction began on Houska Castle which would sit directly over what has been dubbed "the Gateway to Hell". While the outer facade looked perfectly normal, closer inspection of the castle showed this was beyond the ordinary. If one peers through the barred windows on the outside, rather than seeing inside the structure they will instead see a strong stone wall. These windows are simply for decoration to draw attention away from just how reinforced the structure is. There was no water supply, mainly because people were never meant to actually live there and for many years it stood empty. It may have seemed curious to outsiders that this stone fortress sat far away from any travel routes and was seemingly uninhabitable, but the people of the region knew the truth. If one were brave enough to travel inside they will find the religious frescoes one would expect from a medieval castle. If you look closer, however you will see the artwork here depicts strange beasts and demonic entities attacking humans while Christ, St. Michael, and St Christopher are fighting them off.
Of course in the center of Houska Castle is the infamous hole which supposedly leads straight to Hell. It has naturally been sealed up, and the fort's chapel has been built directly on top of it. According to witnesses that has done little to stop the evil within. Many people who have ventured into the castle have reported hearing scratching and screams from beneath the ground they walk on, especially as you get closer to where the pit lies. Adding to the evil in this old fortress, the Second World War saw the invading Nazis set up base in Houska Castles upon hearing the stories of it. They hoped the supernatural energy of the castle would ultimately serve as a source of power.
Even today the people of Doksy witness the supernatural evil said to be in Houska Castle. Most infamously, there is a creature described as a hybrid of a human and a frog, which has been seen within the castle as well as in the forests surrounding it. Those around the castle claim periodically to hear a "chorus of scream" emanating from Gateway to Hell. The Hunting Lodge, which is regularly rented out to people is home to two shadowy entities who seem to be whispering something about a murdered girl. The current owner of the building, Jaromir Simonek and his caretakers have reported experiencing paranormal activity at the castle firsthand. All of them have claimed to see the spirit of a decapitated man stumbling through the courtyard, though they do not have the slightest clue as to the spirit's identity.
Being just 30 miles north of Prague, Houska Castle has attracted a good amount of attention for being a paranormal hot spot. Whether the hole it is built upon is truly the Gateway to Hell or not, there is no denying that supernatural evil lies behind it's walls.
