Skylanders Spyro's Adventure soul gem locations guide

Gem #15: Troll Warehouse

Unlocks: Zook’s “MIRV Mortar” Ability

This one practically can’t be missed. As you make your way through the level, you’ll be asked to complete the minefield map. During your search for the pieces, you’ll reach this area just after completing a crystal laser puzzle. Clear the area of enemies, and simply run onto the bridge to grab the Soul Gem.