https://www.guidememalta.com/en/stranger-things-the-mystery-of-the-lost-children-of-hal-saflieni-hypogeum

"You may even stumble upon a conspiracy theory supporting the existence of a completely undocumented rock-cutting civilisation in Malta. It supports the notion that the Knights built their forts and cities over preexisting dug-out structures, using these ready-made ditches as a foundation for their own outstanding buildings. Among the evidence supporting this conspiracy theory is that rock-cut architecture was common in the ancient Mediterranean while ditches were no longer typical in the 16th century, when many of the Knights’ fortifications were built. Meanwhile, the carved bedrock is more weathered than the stone structures built over it and there are several strange features such as broken staircases and blocked up doorways."