The Earth is a globe.

This can be proven by the fact that you can view the sunset twice.

If you go to a flat area, you can accomplish this.
You can lay down, and view the sunset. Once the sun is out of sight, you can quickly stand up and view it again.

This proves that the Earth has a curvature, and is therefore round. If the Earth was flat, this wouldn't be possible. Luckily, since it is, one can experience the sunset twice.