Historical clue formulations

• Site of an underground pool, maybe — 2021-05-14
• Capri has a blue one — 2020-08-25
• Natural shelter — 2015-05-16
• Cave — 2015-01-01
• Blue ___ — 2007-01-13
• Cave — 2005-09-26
• Cave — 2003-11-24
• Small cavern — 2003-11-18
• Natural hideout — 2000-08-05
• Blue ___ — 1998-12-20
• Capri's Blue _____ — 1995-03-22