Crisis Core: Final Fantasy VII/Seven Wonders Expert

At the start of Chapter 8, talk to the little boy near the Water Tower in Nibelheim to begin the Seven Wonders Expert Side Quest.

Walkthrough
There are seven mysteries in Nibelheim to uncover, each time, you need to report back to the little boy in order to unlock the next one:
 * 1) Examine the Water Tower in Nibelheim to receive the Phoenix materia.