Hi Amina @amina-gojak, I agree with Ronny (@rleder), these appear to carbonate rocks/minerals. We saw some similar structures in Panama. Here is a picture of a limestone ‘tube’ from Lago Alajuela that is similar to the first image in your second set of photos. As Ronny explained, the carbonate dissolves and re-precipitates in ways that give the appearance of something once living, such as a burrow, but are in fact inorganic. Definitely still fun to find though!