Hot air balloons work because hot air rises. If you contain a lot of hot air it will want to rise up into the sky. The secret to hot air balloons and the reason they are able to go up and come down again is because the quantity and temperature of hot air is controlled.

You may wonder how many hot air balloon crashes there are each year but that would be a difficult thing to ascertain since arguably every hot air balloon landing is a controlled crash. As the hot air is released from the balloon it descends towards the ground at a controlled rate but eventually it hits the ground in a controlled crash landing. That sounds more dramatic than it usually is and most times the landing is all part of the exciting experience and remember a hot air balloon is not dependent on having an engine that keeps working like an aircraft does.