Questions & Answers about Ni grimpis sur grandan rokon.
The ending -is marks the past tense in Esperanto.
So:
- grimpi = to climb
- grimpas = climbs / is climbing
- grimpis = climbed
- grimpos = will climb
So Ni grimpis means we climbed.
Sur means on, onto, or on top of, depending on context.
In this sentence, it shows the destination of the climbing: they climbed onto a big rock.
So sur grandan rokon means something like onto a big rock rather than just to a rock in a general sense.