please help find any incorrect prepositions and mistakes in my letter

[Kwfine]

Ivy, Vivian, Jan and I had been to Africa twice last year, which were
great experience for we fours.
Climbing those high mountains which rise above the plain was a lot of fun to us...

I am hesitated, thinking if it is better to say

Climbing those high mountains rise above the plain was a lot of fun to us...

than

Climbing those high mountains rise above the plain was a lot of fun to all of us...

Please help!

Thanks

Kitty
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各位前輩安安, 我是kitty喔!

[Mister Micawber]

.
Ivy, Vivian, Jan and I went to Africa twice last year, which was a great experience. Climbing those high mountains that rise above the plain was a lot of fun for the four of us.
.
_________________
Native English teacher at Mister Micawber's

[Kwfine]

Thanks, Mister Micawber!

May I ask why it is not
"Ivy, Vivian, Jan and I went to Africa twice last year, which were great experience.", because we went to Africa twice.
_________________
各位前輩安安, 我是kitty喔!

[Mister Micawber]

.
You are confusing imagination with grammar. You have two choices:

[We went to Africa twice last year,] which was a great experience.

We went to Africa [twice] last year, which were great experiences.
.
_________________
Native English teacher at Mister Micawber's

[Kwfine]

Thank you so much for the help, Mister Micawber!
_________________
各位前輩安安, 我是kitty喔!