Kiwi's cage was small/medium at first when she was still so little. But when baby Kiwi had grown, her cage (with first and second floor) became too small for her. Earlier this month, she was still contented though.
However, on the night I took home a new hamster with a large cage with tubes I bought for it the other sunday (which I'm not sure if she sensed that the new one has a larger cage

), I noticed that Kiwi suddenly looked unusual and so depressed, that I got worried if she's going to be ill. She barely used her wheel that night when she spent hours on it
So the next day, I went back to the store to buy the very same cute design of cage I bought the night before!

And the moment she went inside in when I got home, she suddenly turned hyper in a good way!
Her sadness turned into an unsually happy mood, that she checked out everytime right away!
She was never jumpy thankfully. I guess that's how sad she was on her first cage

, that all she could think of in the new one was to be happy. And all she did was running so fast everywhere, and rushing in tubes all night!
Then I moved her wheel from the first cage

But she just smelled it at first out of excitement with the tubes

I also gave apple, her favorite, but she still prefered the large cage
Thank you for your replies, you made me not worried about buying a large cage!