I don't know what the real story is, but Egyptian, Peruvian and other ancient architecture using gigantic stones and impossible precision is very mysterious. It appears there is very ancient water erosion indicating the Sphinx may be much older than reported, plus there are actual ancient cities buried which haven't yet been uncovered, like the one discovered in Mexico, or sites that are barely uncovered like Gobekli Tepe in Turkey. The "authorities" are untrustworthy so who knows what they're hiding? No idea about Mars, but it made me think of this. Some people think there were giants. At the least there must be lost building techniques we can't match to this day.