Sorry Big Thumb, but I was pretty sure it was the Masada from the start. With the clue and the picture it was the first thing that came to mind. I was thrown off by the not in the Bible part, but I was still pretty certain.
I didn’t know that it was that place. I don’t think I would have got it before you anyway.
I had to do some research about whether it was mentioned in the bible or not, as this was one of the questions and found this site www.ancientsandals.com/overviews/masada.htm where it states:
“Although Masada is not mentioned in the Bible by name, it is possible that this was David’s place of refuge during his flight from Saul and where he wrote some of his Psalms. If so, David was probably referring to Masada as the “stronghold” (1 Sam 22:4-5; 23:14; 24:22), using it to depict God as his fortress and rock of refuge (Ps 18:2, 31; 71:3; 144:2).”
I visited that place in 1982 and found the story behind it quite unusual.