1. Longyou Caves. Hidden deep within the remote village of Shiyan Beicun in the province of Zhejiang, China, lie the fabled Longyou Caves. At a mere glance, it may seem just like your run-of-the-mill ancient civilization wonder. However, it’s riddled with many mysteries that baffle experts and scientists to this day. Discovered in 1994, the artificial grottoes are said to have been constructed as far back as 2,000 to 3,000 years ago. This puts it on the historical map even earlier than the most prevalent Chinese dynasties. What’s most puzzling is that all the engineering feats demonstrated in making this were simply far beyond what a per-imperial civilization could have accomplished. Since the caves were built to be very spacious both in width and height, the labor force required to build such a phenomenal structure without machines must have been in the thousands, working day and night. Every surface, wall and ceiling must have been painstakingly chiseled with parallel lines. The structural integrity of the caves was so sound that significant degradation is almost absent. Add the fact that it was built in the relative blackness of the cave with only very primitive lighting tools, and we have a very intriguing archaeological mystery. In fact, archaeologists still don’t know who exactly built the caves. The caves were initially found completely flooded, and the builders left no evidence or records of their stay. The only thing left indicative of their culture were very ambiguous stone carvings.