From publisher blurb:
What is a Drop Zone encounter?
A Drop Zone encounter is not an adventure in the usual sense, but is designed as a finite, independent area you can drop into most any campaign world. Each encounter is a geographic area that contains specific components, i.e. structures, events, creatures, items, effects, etc. All components are fully detailed along with several variations.
What a Drop Zone encounter doesn’t have is a specific plotline, an expected outcome. How your PCs react to the components of the encounter or how the components react to the PCs isn’t preordained. You are provided with numerous options and ideas to pick and choose from, all to help you mold this encounter towards your group’s and your campaign’s unique needs.
You can weave each Drop Zone into the storyline of your own home brew campaign or simply use each as a short diversion between adventures. Either way, Drop Zones are a quick and effortless way to spice up the more unremarkable portions of your campaign world.