Here's How:
1. This is so easy! Add chunks of dry ice (solid carbon dioxide) to hot water in a styrofoam or other insulated container.

2. The fog will sink to the ground. You may use a fan on a low setting to move your 'smoke'.

3. The water will cool, so you will need to refresh the hot water to maintain the effect.

4. Room temperature matters - you will get the most fog in a cool room. Have fun!

Tips:
Dry ice is cold enough to give frostbite. Wear protective gloves when handling it.
Larger chunks of dry ice will last longer than smaller ones.
Be aware that extra carbon dioxide is being added to the air. Under some circumstances, this can present an asphyxiation hazard.
Sometimes inexpensive dry ice machines are available, otherwise check party supply stores and shipping companies for availability.
Keep dry ice away from childen, pets, and fools! Adult supervision is required.

What You Need:
Dry Ice (Carbon Dioxide)
Hot Water
Insulated Container