Houska Castle is an early Gothic castle, 47 kilometres (29 mi) north of Prague, in Czechia. It is one of the best preserved castles of the period. Notable features include a predominantly gothic chapel, green chamber with late-gothic paintings, and knight's drawing room.
It was built in the second half of the 13th century probably on the orders of Bohemian ruler Ottokar II of Bohemia during his reign (1253–78) to serve as an administration center from which the extensive royal estates could be managed. Later it passed to the hands of the aristocracy, frequently passing from the ownership of one to another. In 1584–90 it underwent Renaissance-style modifications, losing none of its fortress features as it looks down from a steep rocky cliff. In the 18th century it ceased to serve as a noble residence and fell into a state of disrepair before being renovated in 1823. In 1897 it was purchased by Princess Hohenlohe and in 1924, the times of the First Republic, bought by the President of Škoda, Josef Šimonek. During World War II, the Germans used the castle to perform inhumane experiments on local people or prisoners of war. 
Houska castle, and most specifically the chapel, has been constructed over a large hole in the ground that is allegedly a "gateway to Hell", which was said to be so deep no one could see the bottom of it. Animal-human hybrids were reported to have crawled out of it, and dark-winged, otherworldly creatures flew in its vicinity. Legend has it that when construction began in the castle, all of the inmates that were sentenced to death were offered a pardon if they consented to be lowered by rope into the hole, and report back on what they saw. When the first person was lowered, he began screaming after a few seconds, and when pulled back to the surface he looked as if he had aged 30 years. He had grown wrinkles and his hair had turned white, as old folklore tales state.
Houska castle was built with no fortifications, no water, no kitchen, near no trade routes, and with no occupants at its time of completion. The castle was not built as a residence or as a protective sanctuary, but was instead built because the hole was thought to be a gateway to hell. Thus, by constructing the Gothic building, they were able to keep the demons trapped in the lower level thickest walls closest to the hole of the castle.
Houska Castle was featured on an episode of Ghost Hunters International which aired on SyFy on July 22, 2009. Most Haunted Live visited the castle on March 26, 2010. The French team of paranormal investigators, R.I.P recherches investigations paranormal, investigated the Castle in 2013 in their episode "The Hell Gate" (Episode 2, Season 3).