Monday is Labor Day, an American observance held every September to recognize the achievements of workers. Started in 1882 and codified by Congress in 1894, Labor Day is now seen as the unofficial end of summer. It's also a cause for celebration, because it often means a three-day weekend.

If you're off this weekend, you may be wondering where you can go and what you can do. Here's what's open and closed Monday:

Labor Day is a federal holiday, which means the government closes most of its nonessential offices. All social security offices are closed, as are most states' departments of motor vehicle (DMVs). 

Post offices will be closed, and mail won't be delivered Monday. FedEx Express, Ground, Home Delivery and SmartPost are all closed Monday, too. UPS observes Labor Day, as well.

The Federal Reserve and its branches will be closed Monday. The New York Stock Exchange and Nasdaq will be closed, as will most locations of major bank chains like Bank of America, TD Bank and Chase Bank.

Schools' schedules will vary, but most will be closed on Labor Day. Hospitals and emergency rooms will generally be open, but individual clinics may be closed and specialized staff may be off.

For stores, Labor Day is a great opportunity for sales and promotions. Kmart, Target, CVS and Walmart are all open, according to holidayshoppinghours.com.  Restaurants will be open Monday, as well, including KFC and Wendy's.

Public transit is where things get hairy. On Monday, New York City subways and buses will run on their Sunday schedules. But in Brooklyn, there will be changes on the 2, 3, and 4 lines near Eastern Parkway due to the J'Ouvert parade from 10 a.m.-6 p.m. EDT. In Washington, D.C., trains will run on a Sunday schedule between 7 a.m. and midnight. However, construction will alter the red, orange, blue and silver lines as detailed here.