If you're lucky enough to have a summer house, there still comes a sad moment when your summer luck runs dry and you have to close it for winter. Taking the right precautions can both save you a load of trouble and help you get things together next year.
Start with a thorough cleaning. Trash any varmint-magnets like food, unsealed spices, and stacks of newspapers, a favorite bug breeding ground. Enhance air flow to reduce mustiness. Ways to increase airflow include defrosting your fridge and leaving the door ajar, opening storage-area doors, and flipping pillows and mattresses. Also be sure to cover dust-absorbing furniture like sofas or upholstered chairs with storage tarps.
If freezing conditions are an issue, you'll want a plumber to help shut down the pipes and water heater properly. Fill the toilets, sinks, and other water-using appliances with a mixture of water and anti-freeze to protect drains. Finally, you should shut off the electricity and gas, assuming they are not crucial to any heating, ventilation, or security systems you want to leave running.