Seven Wonders in Nibelheim

Wonder #1: Interact with the water tower in the town square to find a red Materia, unlocking the Phoenix DMW Image. This is missable.

Wonder #2: In the Inn, examine the painting of a girl upstairs. Return later to see the girl disappear. Follow the man who appears to be stashing Gil behind the painting. He will give you 2,000 Gil for your silence.

Wonder #3: Head to Mt. Nibel (northern exit from Outskirts) and defeat three Bombs. Defeat them in the order: Right, Left, Middle, before any explode, to obtain the Gold Shard. If you fail, exit and re-enter the area to try again.

Wonder #4: Solve the riddle of the Laughing Safe in the Shinra Manor. The code is randomized, refer to a dedicated safe code guide for assistance. The reward is a Mastered Vital Slash Materia.

Wonder #5: After progressing the story and playing through events at the Mako Reactor, return to Shinra Manor. Go to the basement and defeat the Sahagin in the upper corner to obtain the Coffin Key. Use this key on the coffin in the southeast room. If you use the wrong coffin, you'll need to retrieve another key.

Wonder #6: During the Chapter when Nibelheim is burning, find the boy outside the Inn. His mother is trapped on the second floor of a burning house. You have one minute to navigate through the burning house to reach her window. The path involves moving forward until you hit an obstacle, then adjusting direction. Once you reach her, guide Zack back out of the house. The reward is an ATK Up++ Materia.

Wonder #7: In Chapter 9, as you leave Shinra Manor with Cloud, you will receive a mail from the Wonder Hunter. Head to the fence in the northeast of the Outskirts to find the final reward, a Wall Materia. This completes the Mail Completionist Trophy/Achievement.