Built in the 13th Century, this castle is built for unknown reasons. It was built with defenses facing in. The windows were fake and there wasn't even a kitchen or water resources. Many locals believed that it was built to keep demons rising from the depth of hell. That the chapel within the walls was placed directly over a pit in which creatures and demons had come out and plagued the local area. After Nazi's occupied the area, more rumors swirled that paranormal investigation was their purpose within the walls. Nowadays the castle is owned by a family and is open for tours and paranormal investigations are welcome. At your own risk. 

Sources:

https://www.history.co.uk/articles/houska-castle-gateway-to-hell

https://www.atlasobscura.com/places/houska-castle

https://unusualplaces.org/houska-castle/#:~:text=Approximately%2030%20miles%20north%20of%20Prague,%20a%20mysterious%20castle%20known

https://www.discoveryuk.com/mysteries/the-real-truth-behind-houska-castle/

https://allthatsinteresting.com/houska-castle

https://thisweekinlibraries.com/the-haunting-beauty-of-houska-castle-exploring-its-dark-legends/#:~:text=Houska%20Castle%20is%20a%20place%20shrouded%20in%20%E2%80%8Dmystery%20and%20macabre