(D) to get on → (D) to get around

Corrected sentence: When travelling to a new city, it's important to ask locals for directions to get around easily.

(A) the most challenging → (A) the more challenging

Corrected sentence: The more challenging the puzzle is, the more satisfying the sense of accomplishment gets.

(C) the more warm → (C) the warmer

Corrected sentence: The colder it gets, the warmer the coat needs to be.

No correction needed

The sentence is correct as written.

(A) At → (A) On

Corrected sentence: On weekends, I love to hang out with my sister and watch movies together.