I’m in the middle of reading this book which says it was real along with another “lost city” called Mu or Lemuria (which existed in the Pacific—Atlantis -> Atlantic). Anyway, the author posits that Atlantis and Mu/Lemuria were destroyed by cataclysmic events including the flood that is referenced in Genesis (Noah and the Ark—that flood).
The way this makes sense is to view the biblical story of the flood (as well as other bible stories) as merely codified versions of much older stories. He does some comparative anthropology in his book and notes that many major/ancient civilizations have a story of a “golden age” followed by a cataclysm and a great flood, which he believes ties it all to an actual flood that occurred sometime prior to 13,000 BC, after which the waters subsided and civilizations began to (re)appear. According to the author, there is also geologic evidence to support the timing of this cataclysm (formation of the Azores, the Himalayas, etc.)
There’s a lot more to the book than just whether Atlantis existed, and it’s basically an exercise in decoding the bulk of human history through the lens of global conspiracy (think The Da Vinci Code), but the dynamics he describes are certainly plausible. He cites the technology required to build the world’s many ancient wonders (transferred from a lost civilization to civilizations on historical record) as one bit of evidence supporting the idea that an advanced civilization existed prior to what we commonly know as the earliest civilizations.
To address your point about having found it already with our modern equipment, the author would probably point to the “interdimensional” nature of existence and the idea that Atlantis and its constituents existed on a higher “astral” frequency than modern day humanity and perhaps were “brought down to earth” and human form following the flood. This would be incredibly far fetched, except for his laying down an earlier premise that what humans can perceive through the senses (i.e. the visible spectrum) represents only the tiniest sliver of the electromagnetic spectrum, which itself is only .005% of what is believed to exist in the universe. (The majority would be dark matter and light matter.)