A Fallen Genius?

There are 10 towers so you'll have to defeat 10 enemies. The first 9 are Rhyos, marked as white triangles on the mini-map. After you defeat each one, it will leave behind a chest. The contents of each chest depend on how successful your calibration attempts were in Chapter 3. For a detailed chart, see Lightning Rod Towers.

After the 9th tower has been cleared, a red arrow on the mini-map will point the way to the 10th tower. When you approach, answer "Let's check it out." to fight Humbaba. Once it has been defeated, you receive Valiant Lustre grid (along with the reward earned from Lightning Rod Towers). Mission Complete!

Walkthrough:
Required: No
Description: Frenzied fiends are feeding off the energy stored in the lightning rod towers. Destroy every last one of the fiends clinging to the towers!
Objective: Defeat the fiends at each tower