Mysterious bottomless pit, see the answer

1. It is located on the seashore of the ancient Greek city of Argos. It is very large and deep, and the amount of seawater injected into the cave every day is more than 30 thousand tons, but it is not filled.

2. 1958, the American Geographical Society sent an expedition to dissolve a durable colored dye in seawater and observe how the dye sank with the seawater. Judging holes by observing where the pigment flows out.

As a result, no dye was found and the mystery was not solved.