成語紀元：成語猜猜，習國文 - Idiom Guess

On this day, I crossed...
When I inexplicably appeared in a wasteland, I was still in shock. I looked up and found that the people here were naked, no, to be precise, they were not wearing clothes! They were wearing veils woven from leaves and had primitive weapons in their hands. What the hell was going on?
The appearance of a cat answered my doubts: by chance, I really traveled to the primitive period. If I want to return to the modern age, I must pass many tests and gradually open up a new era, and the key to open the door of time and space is hidden. In one idiom, now I'm in trouble, can you help me?

[Gathering up ideas] Completing idioms and helping me collect civil engineering
[Cave in the Nest] Build a home and protect my world
【Single Spark】Explore civilization and open up a long history with me

Guess the idiom, guess the idiom.
Come explore with me, feel the charm of idioms, immerse yourself in the changes of history. The vicissitudes of life, I am waiting for you!