Breakdown of В этой пещере мы нашли интересный образец.
мы
we
интересный
interesting
этот
this [f: эта, n: это]
в
in / to (direction)
Questions & Answers about В этой пещере мы нашли интересный образец.
Why is it этой пещере instead of эта пещера?
The phrase в этой пещере tells us where something happened, so it uses the Prepositional case. The feminine word for "this" (эта) changes to этой, and пещера (cave) changes to пещере.
What is the dictionary form of the verb нашли?
The infinitive is найти (to find). It is a perfective verb with a slightly irregular past tense: нашёл for a masculine subject, нашла for feminine, and нашли for plural (like мы here).
Why don't the endings of интересный образец change, even though it's the direct object?
As the direct object of what was found, интересный образец is in the Accusative case. However, because образец is a masculine inanimate noun (a non-living thing), its Accusative form is completely identical to its Nominative (dictionary) form.