Time for action – using empty objects

Our level has a few objects that could use some organization, and Unity makes this easy by letting us create empty GameObjects. An empty object is a perfect container for holding related groups of objects because it doesn't come with any components attached—it's a shell. 

Let's take our ground plane and four walls and group them all under a common empty GameObject:

1. Select Create | Create Empty in the Hierarchy panel and name the new object Environment.
2. Drag and drop the ground plane and the four walls into Environment, making them child objects.
3. Select the Environment empty object and check that its X, Y, and Z positions are all set to 0:

The environment exists in the Hierarchy tab as a parent object, with the arena objects as its children. Now we're able to expand or close the Environment object drop-down list with the arrow icon, making the Hierarchy panel less cluttered.

It...