This is the 626th most frequent Polish word.
istnieje
"Exists" or "there is."
In this sentence, "istnieje" is used to mean "there are" or "exists" to express the presence of reasons.
Istnieje wiele powodów, dla których warto uczyć się języków obcych.
There are many reasons why learning foreign languages is worthwhile.
In this usage, "istnieje" indicates the hypothetical or mythological presence of the treasure according to the legend.
Legenda mówi, że gdzieś na tym terenie istnieje ukryty skarb.
The legend says that somewhere in this area there exists a hidden treasure.
Here, "istnieje" conveys the idea of something being real or present.