This is the 11469th most frequent Polish word.
jaskini
"Cave."
Here, 'jaskini' (cave's) is used in the genitive case after 'eksploracja' (exploration), which governs this case.
Eksploracja jaskini była ekscytująca.
Exploring the cave was exciting.
'Jaskini' is used in the locative case, appropriate after the preposition 'w' (in) indicating the location.
W jaskini znaleziono starożytne malowidła.
Ancient paintings were found in the cave.
Again, 'jaskini' appears in the genitive case, as the preposition 'do' (to) requires this case to denote possession or direction.