Translation of gallstone in German

Then we did a boat trip which started somewhere in the delta and ended somewhere else in the delta. Each couple received a boat and an elderly lady had to row. I did not feel comfortable with that.
We joined the mass and climbed it. The stones were a little slippery and I doubt that this place is accident free. Climbing big slippery stones was not an easy task but we managed it slowly.
The next day we decided to spend on the other side of the mountain range (antiplano), in Bolivia. We didn't have the courage to drive deep into Bolivia, as everyone told us about the bad infrastructure and condition there.