Just as its name implies, the cup tower is a trap built by stacking cups to build a barricade. It's simple to build and simple for the youngest to navigate.
Begin building your base by lining up cups next to each other. Future layers can only be as wide as your base layer allows.
It can be built in front of doorways or hallways.
It can be built tall or short.
To make this obstacle easier...
1. Try using paper cups instead of plastic, they do not make as much noise
2. Don't build the tower as tall.
To make this obstacle more difficult...
1. Disperse metal utensils in the tower, or hide noise makers (such as jingle bells shown in the images below) under the cups.
2. Hang a jingle bell inside a few cups with string.